Fix Support for Collection Expressions

[BrunoJuchli]

This change fixes support for collection expressions like:

Arr<int> arr = [1, 5, 17];

Lst<int> lst = [5, ..arr, 19];

for

• Arr<T>
• Lst<T>
• Seq<T>
• Set<T>

I've chosen these types because the compiler thinks the collection expressions are already supported for these (it compiles), but the resulting collections are always empty.

Collection Initializers Unaffected

This does not fix collection initializers like:

var arr = new Arr<int> { 1, 5, 17 };

This still results in an empty arr.

Implementation

Implemented create methods according to https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-12.0/collection-expressions#create-methods
see commit 9fff3cc

There's also tests for this, see 4505936

Performance Considerations for Set<T>

The ReadOnlySpan<T> passed to the create methods does not implement IEnumerable<T> and thus cannot be passed to existing constructors of Set<T>.
I've compared two options:

• ReadOnlySpan<T>.ToArray()
• foreach loop over ReadOnlySpan<T> which performs Set.TryAdd

Benchmarking showed that the loop is faster for 0 or 1 elements. After that, ToArray() is significantly faster.

Method	N	Mean	Error	StdDev	Rank
CreateLoopSpan	0	12.50 ns	0.278 ns	0.760 ns	1
CreateCopySpanToArray	0	37.68 ns	0.866 ns	2.512 ns	2
CreateLoopSpan	1	57.02 ns	1.170 ns	3.042 ns	3
CreateCopySpanToArray	1	65.10 ns	1.321 ns	3.570 ns	4
CreateLoopSpan	2	232.58 ns	4.624 ns	9.445 ns	6
CreateCopySpanToArray	2	163.08 ns	3.289 ns	8.664 ns	5
CreateLoopSpan	3	400.38 ns	8.034 ns	21.993 ns	8
CreateCopySpanToArray	3	256.85 ns	5.145 ns	13.734 ns	7

Method	N	Mean	Error	StdDev	Rank
CreateLoopSpan	0	12.69 ns	0.279 ns	0.618 ns	1
CreateCopySpanToArray	0	37.90 ns	0.751 ns	1.741 ns	2
CreateLoopSpan	3	371.38 ns	7.354 ns	15.023 ns	4
CreateCopySpanToArray	3	267.78 ns	5.362 ns	15.210 ns	3
CreateLoopSpan	7	1,880.21 ns	36.439 ns	77.655 ns	6
CreateCopySpanToArray	7	1,048.89 ns	20.921 ns	51.319 ns	5
CreateLoopSpan	50	32,824.62 ns	651.136 ns	1,522.010 ns	8
CreateCopySpanToArray	50	17,175.47 ns	343.452 ns	880.400 ns	7

Method	N	Mean	Error	StdDev	Rank
CreateLoopSpan	100	89.48 us	1.758 us	2.347 us	2
CreateCopySpanToArray	100	42.16 us	0.836 us	2.004 us	1
CreateLoopSpan	1000	1,529.97 us	30.239 us	58.260 us	4
CreateCopySpanToArray	1000	768.68 us	14.868 us	18.260 us	3
CreateLoopSpan	10000	23,371.89 us	461.683 us	867.153 us	6
CreateCopySpanToArray	10000	11,363.98 us	209.157 us	436.588 us	5
CreateLoopSpan	100000	391,907.57 us	7,751.993 us	10,348.688 us	8
CreateCopySpanToArray	100000	168,161.03 us	3,542.300 us	10,276.854 us	7

Implementation for ReadOnlySpan<T>.ToArray()

public static Set<T> create<T>(
    ReadOnlySpan<T> items) =>
    new Set<T>(items.ToArray());

Implementation with foreach loop

public static Set<T> create<T>(
    ReadOnlySpan<T> items)
{
    var set = empty<T>();
    foreach (var item in items)
    {
        set = set.TryAdd(item);
    }

    return set;
}

Implementation of Benchmark

See #1323 (comment)

[BrunoJuchli]

Benchmark

using System;
using BenchmarkDotNet.Attributes;

namespace LanguageExt.Benchmarks
{
    [RPlotExporter, RankColumn]
    [GenericTypeArguments(typeof(int))]
    [GenericTypeArguments(typeof(string))]
    public class SetBenchmarks<T>
    {
        [Params(0, 1, 2, 3, 10, 100, 1000, 10000, 100000)]
        public int N;

        T[] values;

        [GlobalSetup]
        public void Setup()
        {
            values = ValuesGenerator.Default.GenerateUniqueValues<T>(N);
        }

        [Benchmark]
        public Set<T> CreateLoopSpan()
        {
            var span = new ReadOnlySpan<T>(values);
            
            return Set.create(span);
        }
        
        [Benchmark]
        public Set<T> CreateCopySpanToArray()
        {
            var span = new ReadOnlySpan<T>(values);

            var array = span.ToArray();
            
            return new Set<T>(array);
        }
    }
}

Note that here I changed Set.create(span) implementation to be:

[Pure]
public static Set<T> create<T>(
    ReadOnlySpan<T> items)
{
    var set = empty<T>();
    foreach (var item in items)
    {
        set = set.TryAdd(item);
    }
}

[BrunoJuchli]

@louthy
I'd be very happy if you could create a v4 release with this change.
I really like what you're doing with v5 but unfortunately we still have a dependency on .net framework in our project - we're working hard at getting rid of it, but it will take another ~2 years :-(
Including this in a v4 Release would go a long way in convincing my boss that it's worth for us to keep up our monthly donations to you (like I said, we will not benefit from v5 for a long time).

Thank you!

[louthy]

I'm really sorry, but I don't have the bandwidth to maintain v4 and v5 (and the nightmare future merge if I keep changing the v4 branch) -- so changes will be for serious bugs without workarounds only.

language-ext has eaten several months of my time recently, which I really should have been putting into building my new startup project (I have meetings lined up with VCs in September, so I'm pushing pretty hard on my project and the stability of v5 right now). I obviously appreciate the donation, but if I need to forego it to make some progress, then I'll have to do that I'm afraid.

This is an MIT licensed project though, so you're well within your rights to fork it and maintain your own version until you're ready to come over to v5. If you need help with the build process then please let me know, but you should just be able to run the following to produce the nuget artefacts:

dotnet restore
dotnet pack LanguageExt.Core -c Release -o ../../artifacts/bin
dotnet pack LanguageExt.Transformers -c Release -o ../../artifacts/bin
dotnet pack LanguageExt.FSharp -c Release -o ../../artifacts/bin
dotnet pack LanguageExt.Parsec -c Release -o ../../artifacts/bin
dotnet pack LanguageExt.Rx -c Release -o ../../artifacts/bin
dotnet pack LanguageExt.Sys -c Release -o ../../artifacts/bin
dotnet pack LanguageExt.SysX -c Release -o ../../artifacts/bin

(I've removed LanguagExt.CodeGen, because that needs some manual intervention, but also is stand-alone and can remain on the current version)

Sorry I can't be more help.

[BrunoJuchli]

@louthy
I do understand and appreciate very much that you've given quick and clear feedback on the matter. ❤️
Also thanks for the build instructions, we may consider forking.

Good luck + success with your new startup!