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active_support_core_extensions.html
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active_support_core_extensions.html
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<h2>Active Support Core Extensions</h2><p>Active Support is the Ruby on Rails component responsible for providing Ruby language extensions, utilities, and other transversal stuff.</p><p>It offers a richer bottom-line at the language level, targeted both at the development of Rails applications, and at the development of Ruby on Rails itself.</p><p>After reading this guide, you will know:</p>
<ul>
<li>What Core Extensions are.</li>
<li>How to load all extensions.</li>
<li>How to cherry-pick just the extensions you want.</li>
<li>What extensions Active Support provides.</li>
</ul>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li>
<a href="#how-to-load-core-extensions">How to Load Core Extensions</a>
<ul>
<li><a href="#stand-alone-active-support">Stand-Alone Active Support</a></li>
<li><a href="#active-support-within-a-ruby-on-rails-application">Active Support Within a Ruby on Rails Application</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-all-objects">Extensions to All Objects</a>
<ul>
<li><a href="#blank-questionmark-and-present-questionmark"><code>blank?</code> and <code>present?</code></a></li>
<li><a href="#presence"><code>presence</code></a></li>
<li><a href="#duplicable-questionmark"><code>duplicable?</code></a></li>
<li><a href="#deep-dup"><code>deep_dup</code></a></li>
<li><a href="#try"><code>try</code></a></li>
<li><a href="#class-eval-args-block"><code>class_eval(*args, &block)</code></a></li>
<li><a href="#acts-like-questionmark-duck"><code>acts_like?(duck)</code></a></li>
<li><a href="#to-param"><code>to_param</code></a></li>
<li><a href="#to-query"><code>to_query</code></a></li>
<li><a href="#with-options"><code>with_options</code></a></li>
<li><a href="#json-support">JSON support</a></li>
<li><a href="#instance-variables">Instance Variables</a></li>
<li><a href="#silencing-warnings-and-exceptions">Silencing Warnings and Exceptions</a></li>
<li><a href="#in-questionmark"><code>in?</code></a></li>
</ul>
</li>
<li>
<a href="#extensions-to-module">Extensions to <code>Module</code></a>
<ul>
<li><a href="#attributes">Attributes</a></li>
<li><a href="#parents">Parents</a></li>
<li><a href="#anonymous">Anonymous</a></li>
<li><a href="#method-delegation">Method Delegation</a></li>
<li><a href="#redefining-methods">Redefining Methods</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-class">Extensions to <code>Class</code></a>
<ul>
<li><a href="#class-attributes">Class Attributes</a></li>
<li><a href="#subclasses-descendants">Subclasses & Descendants</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-string">Extensions to <code>String</code></a>
<ul>
<li><a href="#output-safety">Output Safety</a></li>
<li><a href="#remove"><code>remove</code></a></li>
<li><a href="#squish"><code>squish</code></a></li>
<li><a href="#truncate"><code>truncate</code></a></li>
<li><a href="#truncate-words"><code>truncate_words</code></a></li>
<li><a href="#inquiry"><code>inquiry</code></a></li>
<li><a href="#starts-with-questionmark-and-ends-with-questionmark"><code>starts_with?</code> and <code>ends_with?</code></a></li>
<li><a href="#strip-heredoc"><code>strip_heredoc</code></a></li>
<li><a href="#indent"><code>indent</code></a></li>
<li><a href="#access">Access</a></li>
<li><a href="#inflections">Inflections</a></li>
<li><a href="#extensions-to-string-conversions">Conversions</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-numeric">Extensions to <code>Numeric</code></a>
<ul>
<li><a href="#bytes">Bytes</a></li>
<li><a href="#extensions-to-numeric-time">Time</a></li>
<li><a href="#formatting">Formatting</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-integer">Extensions to <code>Integer</code></a>
<ul>
<li><a href="#multiple-of-questionmark"><code>multiple_of?</code></a></li>
<li><a href="#ordinal"><code>ordinal</code></a></li>
<li><a href="#ordinalize"><code>ordinalize</code></a></li>
<li><a href="#extensions-to-integer-time">Time</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-bigdecimal">Extensions to <code>BigDecimal</code></a>
<ul>
<li><a href="#extensions-to-bigdecimal-to-s"><code>to_s</code></a></li>
</ul>
</li>
<li>
<a href="#extensions-to-enumerable">Extensions to <code>Enumerable</code></a>
<ul>
<li><a href="#sum"><code>sum</code></a></li>
<li><a href="#index-by"><code>index_by</code></a></li>
<li><a href="#index-with"><code>index_with</code></a></li>
<li><a href="#many-questionmark"><code>many?</code></a></li>
<li><a href="#exclude-questionmark"><code>exclude?</code></a></li>
<li><a href="#without"><code>without</code></a></li>
<li><a href="#pluck"><code>pluck</code></a></li>
</ul>
</li>
<li>
<a href="#extensions-to-array">Extensions to <code>Array</code></a>
<ul>
<li><a href="#accessing">Accessing</a></li>
<li><a href="#adding-elements">Adding Elements</a></li>
<li><a href="#extensions-to-array-extracting">Extracting</a></li>
<li><a href="#options-extraction">Options Extraction</a></li>
<li><a href="#extensions-to-array-conversions">Conversions</a></li>
<li><a href="#wrapping">Wrapping</a></li>
<li><a href="#duplicating">Duplicating</a></li>
<li><a href="#grouping">Grouping</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-hash">Extensions to <code>Hash</code></a>
<ul>
<li><a href="#extensions-to-hash-conversions">Conversions</a></li>
<li><a href="#merging">Merging</a></li>
<li><a href="#deep-duplicating">Deep duplicating</a></li>
<li><a href="#working-with-keys">Working with Keys</a></li>
<li><a href="#slicing">Slicing</a></li>
<li><a href="#extensions-to-hash-extracting">Extracting</a></li>
<li><a href="#indifferent-access">Indifferent Access</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-regexp">Extensions to <code>Regexp</code></a>
<ul>
<li><a href="#multiline-questionmark"><code>multiline?</code></a></li>
</ul>
</li>
<li>
<a href="#extensions-to-range">Extensions to <code>Range</code></a>
<ul>
<li><a href="#extensions-to-range-to-s"><code>to_s</code></a></li>
<li><a href="#include-questionmark-and-cover-questionmark"><code>===</code>, <code>include?</code>, and <code>cover?</code></a></li>
<li><a href="#overlaps-questionmark"><code>overlaps?</code></a></li>
</ul>
</li>
<li>
<a href="#extensions-to-date">Extensions to <code>Date</code></a>
<ul>
<li><a href="#extensions-to-date-calculations">Calculations</a></li>
<li><a href="#extensions-to-date-conversions">Conversions</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-datetime">Extensions to <code>DateTime</code></a>
<ul>
<li><a href="#extensions-to-datetime-calculations">Calculations</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-time">Extensions to <code>Time</code></a>
<ul>
<li><a href="#calculations">Calculations</a></li>
<li><a href="#time-constructors">Time Constructors</a></li>
</ul>
</li>
<li>
<a href="#extensions-to-file">Extensions to <code>File</code></a>
<ul>
<li><a href="#atomic-write"><code>atomic_write</code></a></li>
</ul>
</li>
<li>
<a href="#extensions-to-marshal">Extensions to <code>Marshal</code></a>
<ul>
<li><a href="#load"><code>load</code></a></li>
</ul>
</li>
<li><a href="#extensions-to-nameerror">Extensions to <code>NameError</code></a></li>
<li><a href="#extensions-to-loaderror">Extensions to <code>LoadError</code></a></li>
</ol>
</div>
</div>
</div>
<div id="container">
<div class="wrapper">
<div id="mainCol">
<h3 id="how-to-load-core-extensions"><a class="anchorlink" href="#how-to-load-core-extensions">1 How to Load Core Extensions</a></h3><h4 id="stand-alone-active-support"><a class="anchorlink" href="#stand-alone-active-support">1.1 Stand-Alone Active Support</a></h4><p>In order to have a near-zero default footprint, Active Support does not load anything by default. It is broken in small pieces so that you can load just what you need, and also has some convenience entry points to load related extensions in one shot, even everything.</p><p>Thus, after a simple require like:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
require 'active_support'
</pre>
</div>
<p>objects do not even respond to <code>blank?</code>. Let's see how to load its definition.</p><h5 id="cherry-picking-a-definition"><a class="anchorlink" href="#cherry-picking-a-definition">1.1.1 Cherry-picking a Definition</a></h5><p>The most lightweight way to get <code>blank?</code> is to cherry-pick the file that defines it.</p><p>For every single method defined as a core extension this guide has a note that says where such a method is defined. In the case of <code>blank?</code> the note reads:</p><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/blank.rb">active_support/core_ext/object/blank.rb</a></code>.</p></div><p>That means that you can require it like this:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
require 'active_support'
require 'active_support/core_ext/object/blank'
</pre>
</div>
<p>Active Support has been carefully revised so that cherry-picking a file loads only strictly needed dependencies, if any.</p><h5 id="loading-grouped-core-extensions"><a class="anchorlink" href="#loading-grouped-core-extensions">1.1.2 Loading Grouped Core Extensions</a></h5><p>The next level is to simply load all extensions to <code>Object</code>. As a rule of thumb, extensions to <code>SomeClass</code> are available in one shot by loading <code>active_support/core_ext/some_class</code>.</p><p>Thus, to load all extensions to <code>Object</code> (including <code>blank?</code>):</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
require 'active_support'
require 'active_support/core_ext/object'
</pre>
</div>
<h5 id="loading-all-core-extensions"><a class="anchorlink" href="#loading-all-core-extensions">1.1.3 Loading All Core Extensions</a></h5><p>You may prefer just to load all core extensions, there is a file for that:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
require 'active_support'
require 'active_support/core_ext'
</pre>
</div>
<h5 id="loading-all-active-support"><a class="anchorlink" href="#loading-all-active-support">1.1.4 Loading All Active Support</a></h5><p>And finally, if you want to have all Active Support available just issue:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
require 'active_support/all'
</pre>
</div>
<p>That does not even put the entire Active Support in memory upfront indeed, some stuff is configured via <code>autoload</code>, so it is only loaded if used.</p><h4 id="active-support-within-a-ruby-on-rails-application"><a class="anchorlink" href="#active-support-within-a-ruby-on-rails-application">1.2 Active Support Within a Ruby on Rails Application</a></h4><p>A Ruby on Rails application loads all Active Support unless <code>config.active_support.bare</code> is true. In that case, the application will only load what the framework itself cherry-picks for its own needs, and can still cherry-pick itself at any granularity level, as explained in the previous section.</p><h3 id="extensions-to-all-objects"><a class="anchorlink" href="#extensions-to-all-objects">2 Extensions to All Objects</a></h3><h4 id="blank-questionmark-and-present-questionmark"><a class="anchorlink" href="#blank-questionmark-and-present-questionmark">2.1 <code>blank?</code> and <code>present?</code></a></h4><p>The following values are considered to be blank in a Rails application:</p>
<ul>
<li><p><code>nil</code> and <code>false</code>,</p></li>
<li><p>strings composed only of whitespace (see note below),</p></li>
<li><p>empty arrays and hashes, and</p></li>
<li><p>any other object that responds to <code>empty?</code> and is empty.</p></li>
</ul>
<div class="info"><p>The predicate for strings uses the Unicode-aware character class <code>[:space:]</code>, so for example U+2029 (paragraph separator) is considered to be whitespace.</p></div><div class="warning"><p>Note that numbers are not mentioned. In particular, 0 and 0.0 are <strong>not</strong> blank.</p></div><p>For example, this method from <code>ActionController::HttpAuthentication::Token::ControllerMethods</code> uses <code>blank?</code> for checking whether a token is present:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
def authenticate(controller, &login_procedure)
token, options = token_and_options(controller.request)
unless token.blank?
login_procedure.call(token, options)
end
end
</pre>
</div>
<p>The method <code>present?</code> is equivalent to <code>!blank?</code>. This example is taken from <code>ActionDispatch::Http::Cache::Response</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
def set_conditional_cache_control!
return if self["Cache-Control"].present?
...
end
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/blank.rb">active_support/core_ext/object/blank.rb</a></code>.</p></div><h4 id="presence"><a class="anchorlink" href="#presence">2.2 <code>presence</code></a></h4><p>The <code>presence</code> method returns its receiver if <code>present?</code>, and <code>nil</code> otherwise. It is useful for idioms like this:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
host = config[:host].presence || 'localhost'
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/blank.rb">active_support/core_ext/object/blank.rb</a></code>.</p></div><h4 id="duplicable-questionmark"><a class="anchorlink" href="#duplicable-questionmark">2.3 <code>duplicable?</code></a></h4><p>As of Ruby 2.5, most objects can be duplicated via <code>dup</code> or <code>clone</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
"foo".dup # => "foo"
"".dup # => ""
Rational(1).dup # => (1/1)
Complex(0).dup # => (0+0i)
1.method(:+).dup # => TypeError (allocator undefined for Method)
</pre>
</div>
<p>Active Support provides <code>duplicable?</code> to query an object about this:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
"foo".duplicable? # => true
"".duplicable? # => true
Rational(1).duplicable? # => true
Complex(1).duplicable? # => true
1.method(:+).duplicable? # => false
</pre>
</div>
<p><code>duplicable?</code> matches the current Ruby version's <code>dup</code> behavior,
so results will vary according the version of Ruby you're using.
In Ruby 2.4, for example, Complex and Rational are not duplicable:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
Rational(1).duplicable? # => false
Complex(1).duplicable? # => false
</pre>
</div>
<div class="warning"><p>Any class can disallow duplication by removing <code>dup</code> and <code>clone</code> or raising exceptions from them. Thus only <code>rescue</code> can tell whether a given arbitrary object is duplicable. <code>duplicable?</code> depends on the hard-coded list above, but it is much faster than <code>rescue</code>. Use it only if you know the hard-coded list is enough in your use case.</p></div><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/duplicable.rb">active_support/core_ext/object/duplicable.rb</a></code>.</p></div><h4 id="deep-dup"><a class="anchorlink" href="#deep-dup">2.4 <code>deep_dup</code></a></h4><p>The <code>deep_dup</code> method returns a deep copy of a given object. Normally, when you <code>dup</code> an object that contains other objects, Ruby does not <code>dup</code> them, so it creates a shallow copy of the object. If you have an array with a string, for example, it will look like this:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
array = ['string']
duplicate = array.dup
duplicate.push 'another-string'
# the object was duplicated, so the element was added only to the duplicate
array # => ['string']
duplicate # => ['string', 'another-string']
duplicate.first.gsub!('string', 'foo')
# first element was not duplicated, it will be changed in both arrays
array # => ['foo']
duplicate # => ['foo', 'another-string']
</pre>
</div>
<p>As you can see, after duplicating the <code>Array</code> instance, we got another object, therefore we can modify it and the original object will stay unchanged. This is not true for array's elements, however. Since <code>dup</code> does not make deep copy, the string inside the array is still the same object.</p><p>If you need a deep copy of an object, you should use <code>deep_dup</code>. Here is an example:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
array = ['string']
duplicate = array.deep_dup
duplicate.first.gsub!('string', 'foo')
array # => ['string']
duplicate # => ['foo']
</pre>
</div>
<p>If the object is not duplicable, <code>deep_dup</code> will just return it:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
number = 1
duplicate = number.deep_dup
number.object_id == duplicate.object_id # => true
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/deep_dup.rb">active_support/core_ext/object/deep_dup.rb</a></code>.</p></div><h4 id="try"><a class="anchorlink" href="#try">2.5 <code>try</code></a></h4><p>When you want to call a method on an object only if it is not <code>nil</code>, the simplest way to achieve it is with conditional statements, adding unnecessary clutter. The alternative is to use <code>try</code>. <code>try</code> is like <code>Object#send</code> except that it returns <code>nil</code> if sent to <code>nil</code>.</p><p>Here is an example:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# without try
unless @number.nil?
@number.next
end
# with try
@number.try(:next)
</pre>
</div>
<p>Another example is this code from <code>ActiveRecord::ConnectionAdapters::AbstractAdapter</code> where <code>@logger</code> could be <code>nil</code>. You can see that the code uses <code>try</code> and avoids an unnecessary check.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
def log_info(sql, name, ms)
if @logger.try(:debug?)
name = '%s (%.1fms)' % [name || 'SQL', ms]
@logger.debug(format_log_entry(name, sql.squeeze(' ')))
end
end
</pre>
</div>
<p><code>try</code> can also be called without arguments but a block, which will only be executed if the object is not nil:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
@person.try { |p| "#{p.first_name} #{p.last_name}" }
</pre>
</div>
<p>Note that <code>try</code> will swallow no-method errors, returning nil instead. If you want to protect against typos, use <code>try!</code> instead:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
@number.try(:nest) # => nil
@number.try!(:nest) # NoMethodError: undefined method `nest' for 1:Integer
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/try.rb">active_support/core_ext/object/try.rb</a></code>.</p></div><h4 id="class-eval-args-block"><a class="anchorlink" href="#class-eval-args-block">2.6 <code>class_eval(*args, &block)</code></a></h4><p>You can evaluate code in the context of any object's singleton class using <code>class_eval</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Proc
def bind(object)
block, time = self, Time.current
object.class_eval do
method_name = "__bind_#{time.to_i}_#{time.usec}"
define_method(method_name, &block)
method = instance_method(method_name)
remove_method(method_name)
method
end.bind(object)
end
end
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/kernel/singleton_class.rb">active_support/core_ext/kernel/singleton_class.rb</a></code>.</p></div><h4 id="acts-like-questionmark-duck"><a class="anchorlink" href="#acts-like-questionmark-duck">2.7 <code>acts_like?(duck)</code></a></h4><p>The method <code>acts_like?</code> provides a way to check whether some class acts like some other class based on a simple convention: a class that provides the same interface as <code>String</code> defines</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
def acts_like_string?
end
</pre>
</div>
<p>which is only a marker, its body or return value are irrelevant. Then, client code can query for duck-type-safeness this way:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
some_klass.acts_like?(:string)
</pre>
</div>
<p>Rails has classes that act like <code>Date</code> or <code>Time</code> and follow this contract.</p><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/acts_like.rb">active_support/core_ext/object/acts_like.rb</a></code>.</p></div><h4 id="to-param"><a class="anchorlink" href="#to-param">2.8 <code>to_param</code></a></h4><p>All objects in Rails respond to the method <code>to_param</code>, which is meant to return something that represents them as values in a query string, or as URL fragments.</p><p>By default <code>to_param</code> just calls <code>to_s</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
7.to_param # => "7"
</pre>
</div>
<p>The return value of <code>to_param</code> should <strong>not</strong> be escaped:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
"Tom & Jerry".to_param # => "Tom & Jerry"
</pre>
</div>
<p>Several classes in Rails overwrite this method.</p><p>For example <code>nil</code>, <code>true</code>, and <code>false</code> return themselves. <code>Array#to_param</code> calls <code>to_param</code> on the elements and joins the result with "/":</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
[0, true, String].to_param # => "0/true/String"
</pre>
</div>
<p>Notably, the Rails routing system calls <code>to_param</code> on models to get a value for the <code>:id</code> placeholder. <code>ActiveRecord::Base#to_param</code> returns the <code>id</code> of a model, but you can redefine that method in your models. For example, given</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class User
def to_param
"#{id}-#{name.parameterize}"
end
end
</pre>
</div>
<p>we get:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
user_path(@user) # => "/users/357-john-smith"
</pre>
</div>
<div class="warning"><p>Controllers need to be aware of any redefinition of <code>to_param</code> because when a request like that comes in "357-john-smith" is the value of <code>params[:id]</code>.</p></div><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/to_param.rb">active_support/core_ext/object/to_param.rb</a></code>.</p></div><h4 id="to-query"><a class="anchorlink" href="#to-query">2.9 <code>to_query</code></a></h4><p>Except for hashes, given an unescaped <code>key</code> this method constructs the part of a query string that would map such key to what <code>to_param</code> returns. For example, given</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class User
def to_param
"#{id}-#{name.parameterize}"
end
end
</pre>
</div>
<p>we get:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
current_user.to_query('user') # => "user=357-john-smith"
</pre>
</div>
<p>This method escapes whatever is needed, both for the key and the value:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
account.to_query('company[name]')
# => "company%5Bname%5D=Johnson+%26+Johnson"
</pre>
</div>
<p>so its output is ready to be used in a query string.</p><p>Arrays return the result of applying <code>to_query</code> to each element with <code>key[]</code> as key, and join the result with "&":</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
[3.4, -45.6].to_query('sample')
# => "sample%5B%5D=3.4&sample%5B%5D=-45.6"
</pre>
</div>
<p>Hashes also respond to <code>to_query</code> but with a different signature. If no argument is passed a call generates a sorted series of key/value assignments calling <code>to_query(key)</code> on its values. Then it joins the result with "&":</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
{c: 3, b: 2, a: 1}.to_query # => "a=1&b=2&c=3"
</pre>
</div>
<p>The method <code>Hash#to_query</code> accepts an optional namespace for the keys:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
{id: 89, name: "John Smith"}.to_query('user')
# => "user%5Bid%5D=89&user%5Bname%5D=John+Smith"
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/to_query.rb">active_support/core_ext/object/to_query.rb</a></code>.</p></div><h4 id="with-options"><a class="anchorlink" href="#with-options">2.10 <code>with_options</code></a></h4><p>The method <code>with_options</code> provides a way to factor out common options in a series of method calls.</p><p>Given a default options hash, <code>with_options</code> yields a proxy object to a block. Within the block, methods called on the proxy are forwarded to the receiver with their options merged. For example, you get rid of the duplication in:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Account < ApplicationRecord
has_many :customers, dependent: :destroy
has_many :products, dependent: :destroy
has_many :invoices, dependent: :destroy
has_many :expenses, dependent: :destroy
end
</pre>
</div>
<p>this way:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Account < ApplicationRecord
with_options dependent: :destroy do |assoc|
assoc.has_many :customers
assoc.has_many :products
assoc.has_many :invoices
assoc.has_many :expenses
end
end
</pre>
</div>
<p>That idiom may convey <em>grouping</em> to the reader as well. For example, say you want to send a newsletter whose language depends on the user. Somewhere in the mailer you could group locale-dependent bits like this:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
I18n.with_options locale: user.locale, scope: "newsletter" do |i18n|
subject i18n.t :subject
body i18n.t :body, user_name: user.name
end
</pre>
</div>
<div class="info"><p>Since <code>with_options</code> forwards calls to its receiver they can be nested. Each nesting level will merge inherited defaults in addition to their own.</p></div><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/with_options.rb">active_support/core_ext/object/with_options.rb</a></code>.</p></div><h4 id="json-support"><a class="anchorlink" href="#json-support">2.11 JSON support</a></h4><p>Active Support provides a better implementation of <code>to_json</code> than the <code>json</code> gem ordinarily provides for Ruby objects. This is because some classes, like <code>Hash</code>, <code>OrderedHash</code> and <code>Process::Status</code> need special handling in order to provide a proper JSON representation.</p><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/json.rb">active_support/core_ext/object/json.rb</a></code>.</p></div><h4 id="instance-variables"><a class="anchorlink" href="#instance-variables">2.12 Instance Variables</a></h4><p>Active Support provides several methods to ease access to instance variables.</p><h5 id="instance-values"><a class="anchorlink" href="#instance-values">2.12.1 <code>instance_values</code></a></h5><p>The method <code>instance_values</code> returns a hash that maps instance variable names without "@" to their
corresponding values. Keys are strings:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class C
def initialize(x, y)
@x, @y = x, y
end
end
C.new(0, 1).instance_values # => {"x" => 0, "y" => 1}
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/instance_variables.rb">active_support/core_ext/object/instance_variables.rb</a></code>.</p></div><h5 id="instance-variable-names"><a class="anchorlink" href="#instance-variable-names">2.12.2 <code>instance_variable_names</code></a></h5><p>The method <code>instance_variable_names</code> returns an array. Each name includes the "@" sign.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class C
def initialize(x, y)
@x, @y = x, y
end
end
C.new(0, 1).instance_variable_names # => ["@x", "@y"]
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/instance_variables.rb">active_support/core_ext/object/instance_variables.rb</a></code>.</p></div><h4 id="silencing-warnings-and-exceptions"><a class="anchorlink" href="#silencing-warnings-and-exceptions">2.13 Silencing Warnings and Exceptions</a></h4><p>The methods <code>silence_warnings</code> and <code>enable_warnings</code> change the value of <code>$VERBOSE</code> accordingly for the duration of their block, and reset it afterwards:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
silence_warnings { Object.const_set "RAILS_DEFAULT_LOGGER", logger }
</pre>
</div>
<p>Silencing exceptions is also possible with <code>suppress</code>. This method receives an arbitrary number of exception classes. If an exception is raised during the execution of the block and is <code>kind_of?</code> any of the arguments, <code>suppress</code> captures it and returns silently. Otherwise the exception is not captured:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# If the user is locked, the increment is lost, no big deal.
suppress(ActiveRecord::StaleObjectError) do
current_user.increment! :visits
end
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/kernel/reporting.rb">active_support/core_ext/kernel/reporting.rb</a></code>.</p></div><h4 id="in-questionmark"><a class="anchorlink" href="#in-questionmark">2.14 <code>in?</code></a></h4><p>The predicate <code>in?</code> tests if an object is included in another object. An <code>ArgumentError</code> exception will be raised if the argument passed does not respond to <code>include?</code>.</p><p>Examples of <code>in?</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
1.in?([1,2]) # => true
"lo".in?("hello") # => true
25.in?(30..50) # => false
1.in?(1) # => ArgumentError
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/object/inclusion.rb">active_support/core_ext/object/inclusion.rb</a></code>.</p></div><h3 id="extensions-to-module"><a class="anchorlink" href="#extensions-to-module">3 Extensions to <code>Module</code></a></h3><h4 id="attributes"><a class="anchorlink" href="#attributes">3.1 Attributes</a></h4><h5 id="alias-attribute"><a class="anchorlink" href="#alias-attribute">3.1.1 <code>alias_attribute</code></a></h5><p>Model attributes have a reader, a writer, and a predicate. You can alias a model attribute having the corresponding three methods defined for you in one shot. As in other aliasing methods, the new name is the first argument, and the old name is the second (one mnemonic is that they go in the same order as if you did an assignment):</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class User < ApplicationRecord
# You can refer to the email column as "login".
# This can be meaningful for authentication code.
alias_attribute :login, :email
end
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/aliasing.rb">active_support/core_ext/module/aliasing.rb</a></code>.</p></div><h5 id="internal-attributes"><a class="anchorlink" href="#internal-attributes">3.1.2 Internal Attributes</a></h5><p>When you are defining an attribute in a class that is meant to be subclassed, name collisions are a risk. That's remarkably important for libraries.</p><p>Active Support defines the macros <code>attr_internal_reader</code>, <code>attr_internal_writer</code>, and <code>attr_internal_accessor</code>. They behave like their Ruby built-in <code>attr_*</code> counterparts, except they name the underlying instance variable in a way that makes collisions less likely.</p><p>The macro <code>attr_internal</code> is a synonym for <code>attr_internal_accessor</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# library
class ThirdPartyLibrary::Crawler
attr_internal :log_level
end
# client code
class MyCrawler < ThirdPartyLibrary::Crawler
attr_accessor :log_level
end
</pre>
</div>
<p>In the previous example it could be the case that <code>:log_level</code> does not belong to the public interface of the library and it is only used for development. The client code, unaware of the potential conflict, subclasses and defines its own <code>:log_level</code>. Thanks to <code>attr_internal</code> there's no collision.</p><p>By default the internal instance variable is named with a leading underscore, <code>@_log_level</code> in the example above. That's configurable via <code>Module.attr_internal_naming_format</code> though, you can pass any <code>sprintf</code>-like format string with a leading <code>@</code> and a <code>%s</code> somewhere, which is where the name will be placed. The default is <code>"@_%s"</code>.</p><p>Rails uses internal attributes in a few spots, for examples for views:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module ActionView
class Base
attr_internal :captures
attr_internal :request, :layout
attr_internal :controller, :template
end
end
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/attr_internal.rb">active_support/core_ext/module/attr_internal.rb</a></code>.</p></div><h5 id="module-attributes"><a class="anchorlink" href="#module-attributes">3.1.3 Module Attributes</a></h5><p>The macros <code>mattr_reader</code>, <code>mattr_writer</code>, and <code>mattr_accessor</code> are the same as the <code>cattr_*</code> macros defined for class. In fact, the <code>cattr_*</code> macros are just aliases for the <code>mattr_*</code> macros. Check <a href="#class-attributes">Class Attributes</a>.</p><p>For example, the dependencies mechanism uses them:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module ActiveSupport
module Dependencies
mattr_accessor :warnings_on_first_load
mattr_accessor :history
mattr_accessor :loaded
mattr_accessor :mechanism
mattr_accessor :load_paths
mattr_accessor :load_once_paths
mattr_accessor :autoloaded_constants
mattr_accessor :explicitly_unloadable_constants
mattr_accessor :constant_watch_stack
mattr_accessor :constant_watch_stack_mutex
end
end
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/attribute_accessors.rb">active_support/core_ext/module/attribute_accessors.rb</a></code>.</p></div><h4 id="parents"><a class="anchorlink" href="#parents">3.2 Parents</a></h4><h5 id="module-parent"><a class="anchorlink" href="#module-parent">3.2.1 <code>module_parent</code></a></h5><p>The <code>module_parent</code> method on a nested named module returns the module that contains its corresponding constant:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module X
module Y
module Z
end
end
end
M = X::Y::Z
X::Y::Z.module_parent # => X::Y
M.module_parent # => X::Y
</pre>
</div>
<p>If the module is anonymous or belongs to the top-level, <code>module_parent</code> returns <code>Object</code>.</p><div class="warning"><p>Note that in that case <code>module_parent_name</code> returns <code>nil</code>.</p></div><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/introspection.rb">active_support/core_ext/module/introspection.rb</a></code>.</p></div><h5 id="module-parent-name"><a class="anchorlink" href="#module-parent-name">3.2.2 <code>module_parent_name</code></a></h5><p>The <code>module_parent_name</code> method on a nested named module returns the fully qualified name of the module that contains its corresponding constant:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module X
module Y
module Z
end
end
end
M = X::Y::Z
X::Y::Z.module_parent_name # => "X::Y"
M.module_parent_name # => "X::Y"
</pre>
</div>
<p>For top-level or anonymous modules <code>module_parent_name</code> returns <code>nil</code>.</p><div class="warning"><p>Note that in that case <code>module_parent</code> returns <code>Object</code>.</p></div><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/introspection.rb">active_support/core_ext/module/introspection.rb</a></code>.</p></div><h5 id="module-parents"><a class="anchorlink" href="#module-parents">3.2.3 <code>module_parents</code></a></h5><p>The method <code>module_parents</code> calls <code>module_parent</code> on the receiver and upwards until <code>Object</code> is reached. The chain is returned in an array, from bottom to top:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module X
module Y
module Z
end
end
end
M = X::Y::Z
X::Y::Z.module_parents # => [X::Y, X, Object]
M.module_parents # => [X::Y, X, Object]
</pre>
</div>
<div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/introspection.rb">active_support/core_ext/module/introspection.rb</a></code>.</p></div><h4 id="anonymous"><a class="anchorlink" href="#anonymous">3.3 Anonymous</a></h4><p>A module may or may not have a name:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module M
end
M.name # => "M"
N = Module.new
N.name # => "N"
Module.new.name # => nil
</pre>
</div>
<p>You can check whether a module has a name with the predicate <code>anonymous?</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module M
end
M.anonymous? # => false
Module.new.anonymous? # => true
</pre>
</div>
<p>Note that being unreachable does not imply being anonymous:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module M
end
m = Object.send(:remove_const, :M)
m.anonymous? # => false
</pre>
</div>
<p>though an anonymous module is unreachable by definition.</p><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/anonymous.rb">active_support/core_ext/module/anonymous.rb</a></code>.</p></div><h4 id="method-delegation"><a class="anchorlink" href="#method-delegation">3.4 Method Delegation</a></h4><h5 id="delegate"><a class="anchorlink" href="#delegate">3.4.1 <code>delegate</code></a></h5><p>The macro <code>delegate</code> offers an easy way to forward methods.</p><p>Let's imagine that users in some application have login information in the <code>User</code> model but name and other data in a separate <code>Profile</code> model:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class User < ApplicationRecord
has_one :profile
end
</pre>
</div>
<p>With that configuration you get a user's name via their profile, <code>user.profile.name</code>, but it could be handy to still be able to access such attribute directly:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class User < ApplicationRecord
has_one :profile
def name
profile.name
end
end
</pre>
</div>
<p>That is what <code>delegate</code> does for you:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class User < ApplicationRecord
has_one :profile
delegate :name, to: :profile
end
</pre>
</div>
<p>It is shorter, and the intention more obvious.</p><p>The method must be public in the target.</p><p>The <code>delegate</code> macro accepts several methods:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
delegate :name, :age, :address, :twitter, to: :profile
</pre>
</div>
<p>When interpolated into a string, the <code>:to</code> option should become an expression that evaluates to the object the method is delegated to. Typically a string or symbol. Such an expression is evaluated in the context of the receiver:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# delegates to the Rails constant
delegate :logger, to: :Rails
# delegates to the receiver's class
delegate :table_name, to: :class
</pre>
</div>
<div class="warning"><p>If the <code>:prefix</code> option is <code>true</code> this is less generic, see below.</p></div><p>By default, if the delegation raises <code>NoMethodError</code> and the target is <code>nil</code> the exception is propagated. You can ask that <code>nil</code> is returned instead with the <code>:allow_nil</code> option:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
delegate :name, to: :profile, allow_nil: true
</pre>
</div>
<p>With <code>:allow_nil</code> the call <code>user.name</code> returns <code>nil</code> if the user has no profile.</p><p>The option <code>:prefix</code> adds a prefix to the name of the generated method. This may be handy for example to get a better name:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
delegate :street, to: :address, prefix: true
</pre>
</div>
<p>The previous example generates <code>address_street</code> rather than <code>street</code>.</p><div class="warning"><p>Since in this case the name of the generated method is composed of the target object and target method names, the <code>:to</code> option must be a method name.</p></div><p>A custom prefix may also be configured:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
delegate :size, to: :attachment, prefix: :avatar
</pre>
</div>
<p>In the previous example the macro generates <code>avatar_size</code> rather than <code>size</code>.</p><p>The option <code>:private</code> changes methods scope:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
delegate :date_of_birth, to: :profile, private: true
</pre>
</div>
<p>The delegated methods are public by default. Pass <code>private: true</code> to change that.</p><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/delegation.rb">active_support/core_ext/module/delegation.rb</a></code>.</p></div><h5 id="delegate-missing-to"><a class="anchorlink" href="#delegate-missing-to">3.4.2 <code>delegate_missing_to</code></a></h5><p>Imagine you would like to delegate everything missing from the <code>User</code> object,
to the <code>Profile</code> one. The <code>delegate_missing_to</code> macro lets you implement this
in a breeze:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class User < ApplicationRecord
has_one :profile
delegate_missing_to :profile
end
</pre>
</div>
<p>The target can be anything callable within the object, e.g. instance variables,
methods, constants, etc. Only the public methods of the target are delegated.</p><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/delegation.rb">active_support/core_ext/module/delegation.rb</a></code>.</p></div><h4 id="redefining-methods"><a class="anchorlink" href="#redefining-methods">3.5 Redefining Methods</a></h4><p>There are cases where you need to define a method with <code>define_method</code>, but don't know whether a method with that name already exists. If it does, a warning is issued if they are enabled. No big deal, but not clean either.</p><p>The method <code>redefine_method</code> prevents such a potential warning, removing the existing method before if needed.</p><p>You can also use <code>silence_redefinition_of_method</code> if you need to define
the replacement method yourself (because you're using <code>delegate</code>, for
example).</p><div class="note"><p>Defined in <code><a href="https://github.com/rails/rails/tree/d17eabd6c860bf31b3362fd89f6166dd7854a5c0/activesupport/lib/active_support/core_ext/module/redefine_method.rb">active_support/core_ext/module/redefine_method.rb</a></code>.</p></div><h3 id="extensions-to-class"><a class="anchorlink" href="#extensions-to-class">4 Extensions to <code>Class</code></a></h3><h4 id="class-attributes"><a class="anchorlink" href="#class-attributes">4.1 Class Attributes</a></h4><h5 id="class-attribute"><a class="anchorlink" href="#class-attribute">4.1.1 <code>class_attribute</code></a></h5><p>The method <code>class_attribute</code> declares one or more inheritable class attributes that can be overridden at any level down the hierarchy.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class A
class_attribute :x
end
class B < A; end
class C < B; end
A.x = :a
B.x # => :a
C.x # => :a
B.x = :b
A.x # => :a
C.x # => :b
C.x = :c
A.x # => :a
B.x # => :b
</pre>
</div>
<p>For example <code>ActionMailer::Base</code> defines:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class_attribute :default_params
self.default_params = {
mime_version: "1.0",
charset: "UTF-8",
content_type: "text/plain",
parts_order: [ "text/plain", "text/enriched", "text/html" ]
}.freeze
</pre>
</div>
<p>They can also be accessed and overridden at the instance level.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
A.x = 1
a1 = A.new
a2 = A.new
a2.x = 2
a1.x # => 1, comes from A
a2.x # => 2, overridden in a2
</pre>
</div>
<p>The generation of the writer instance method can be prevented by setting the option <code>:instance_writer</code> to <code>false</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
module ActiveRecord
class Base
class_attribute :table_name_prefix, instance_writer: false, default: "my"
end
end
</pre>
</div>
<p>A model may find that option useful as a way to prevent mass-assignment from setting the attribute.</p><p>The generation of the reader instance method can be prevented by setting the option <code>:instance_reader</code> to <code>false</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class A
class_attribute :x, instance_reader: false
end
A.new.x = 1