Dependencies

Dependencies

In Erlang/OTP you specify the dependencies of your OTPApplication in the applications tuple of the application metadata. This information is mined to provide a list of applications that are required by your release.

There is a problem with this though. There is no way to specify version requirements in this application tuple. There is no way to indicate to an app consumer which versions of a dependency are valid with your OTPApplication.

Sinan solves this in two ways. One way is via an extension to the OTPApplication metadata. The other way is via a similar entry in the sinan.config. They both use the exact same syntax that we will describe below.

Constraining Dependency Versions

To constrain the versions of set of dependencies that you rely on you must add a dep_constraints tuple to either the OTPApplication dotapp file or the sinan.config. The dep_constraints tuple contains a list of dependency constraints for the OTPApplication in the case of the dotapp or for the entire project in the case of the sinan.config. An individual dependency constraint may look as follows.

{<app-name>, <version>, <type>}

or

{<app-name>, <version 1>, <version 2>, <type>}

or

{<app-name>, <version>}

In the above case type may be one of the following

• gte: greater than or equal
• lte: less than or equal
• lt: less than
• gt: greater than
• eql: equal
• between: between two versions

between is the specifier that takes two versions. So if we depended on my_app between versions 0.1 and 5.0 we would have the entry:

 {my_foo, "0.1", "5.0", between}

that would provide the constraints we need.

The form {<app-name>, <version>} is exactly equivalent to {<app-name>, <version>, eql} and is provided as a convenience.

Lets look at a complete example used in sinan itself. This is from sinan's sinan.config.

{dep_constraints,
 [{cucumberl, "0.0.4", gte},
  {erlware_commons, "0.6.0", gte},
  {getopt, "0.0.1", gte}]}.

This is specifying the versions for the entire sinan project.