Support lambda expressions and method groups as `var` initializers by cston · Pull Request #55132 · dotnet/roslyn

cston · 2021-07-27T03:12:21Z

var d1 = Program.Main;
var d2 = () => { };

Proposal: lambda-improvements.md
Test plan: #52192

jcouv · 2021-07-27T06:36:29Z

+                // (7,28): error CS0446: Foreach cannot operate on a 'anonymous method'. Did you intend to invoke the 'anonymous method'?
+                //         foreach (var d3 in delegate () { }) { }
+                Diagnostic(ErrorCode.ERR_AnonMethGrpInForEach, "delegate () { }").WithArguments("anonymous method").WithLocation(7, 28));
+        }


nit: consider another similar negative test with deconstruction declaration (var x, var y) = ... #Closed

Also, something like (Action a, var b) = (null, () => {}); (I assume should work per spec, but may not work in current implementation)

Please check GetTypeInfo and GetDeclaredSymbol in one of the positive tests

Consider including a test with a non-simple signature (error)

Added tests. Logged #55139 to investigate support for implicitly-typed variables in tuples and deconstruction.

jcouv · 2021-07-27T06:45:52Z

-                //         var m = Main; // CS0815
-                Diagnostic(ErrorCode.ERR_ImplicitlyTypedVariableAssignedBadValue, "m = Main").WithArguments("method group"),
-                // (7,13): error CS0815: Cannot assign lambda expression to an implicitly-typed variable
+                // (7,17): error CS8917: The delegate type could not be inferred.


Comment in var m = Main; // CS0815 is out-of-date #Closed

jcouv

Done with review pass (iteration 1)

jcouv

LGTM Thanks (iteration 2). How do you want to track the deconstruction issue?

jcouv · 2021-07-27T16:08:04Z

@333fred @dotnet/roslyn-compiler for a second review. Thanks

cston · 2021-07-27T16:33:22Z

How do you want to track the deconstruction issue?

Logged #55139.

333fred · 2021-07-27T17:50:13Z

Looking.

333fred · 2021-07-27T17:53:12Z

    public void IAnonymousFunctionExpression_UnboundLambdaAsVar_HasValidLambdaExpressionTree()

Nit: consider renaming to BoundLambda

Refers to: src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests_IAnonymousFunctionExpression.cs:190 in a884c74. [](commit_id = a884c74, deletion_comment = False)

333fred · 2021-07-27T17:54:39Z


            var variableDeclarationGroupOperation = (IVariableDeclarationGroupOperation)semanticModel.GetOperation(variableDeclaration);
-            var variableTreeLambdaOperation = (IAnonymousFunctionOperation)variableDeclarationGroupOperation.Declarations.Single().Declarators.Single().Initializer.Value;
+            var variableTreeLambdaOperation = ((IDelegateCreationOperation)variableDeclarationGroupOperation.Declarations.Single().Declarators.Single().Initializer.Value).Target;


IDelegateCreationOperation

I don't think this is keeping the test correct. Please break the test in a different fashion, such as removing the F() definition so the body is still unbound.

Will add to the next PR, thanks.

333fred · 2021-07-27T17:55:35Z

    public void InvalidLambdaBinding_UnboundLambda()

No longer correctly named, and probably not the correct location for this either, since it's no longer invalid. This test can probably just be removed.

Refers to: src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests_InvalidExpression.cs:333 in a884c74. [](commit_id = a884c74, deletion_comment = False)

333fred · 2021-07-27T17:56:15Z

    public void InvalidLambdaBinding_LambdaExpression()

Same comment.

Refers to: src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests_InvalidExpression.cs:375 in a884c74. [](commit_id = a884c74, deletion_comment = False)

333fred · 2021-07-27T18:03:10Z

+        }
+
+        [Fact]
+        public void ImplicitlyTypedVariables_04()


ImplicitlyTypedVariables_04

Would it be worth making a version of this test where Action inherits from IDisposable?

333fred · 2021-07-27T18:06:31Z

+    static void Main()
+    {
+        var d1 = F;
+        var d2 = (ref int x) => x;


Consider expanding these negative tests with ref returns as well.

333fred

I'm not going to block on any of my test suggestions, but please make sure they're in the next PR.

cston · 2021-07-27T18:21:04Z

    public void IAnonymousFunctionExpression_UnboundLambdaAsVar_HasValidLambdaExpressionTree()

Will add to next PR.

In reply to: 887712078

Refers to: src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests_IAnonymousFunctionExpression.cs:190 in a884c74. [](commit_id = a884c74, deletion_comment = False)

cston · 2021-07-27T18:24:33Z

    public void InvalidLambdaBinding_UnboundLambda()

Will leave these tests here, to catch any regressions, but I'll rename the tests.

In reply to: 887713598

Refers to: src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests_InvalidExpression.cs:333 in a884c74. [](commit_id = a884c74, deletion_comment = False)

davidfowl · 2021-07-29T06:01:31Z

Tell me when this is merged 😄 into a VS build.

oskardudycz · 2021-07-29T06:41:23Z

@cston, a small correction. The link to the proposal should be https://github.com/dotnet/csharplang/blob/main/proposals/csharp-10.0/lambda-improvements.md.
This looks neat! 😄

ghost added the Area-Compilers label Jul 27, 2021

Support lambda expressions and method groups as 'var' initializers

078fdcd

cston force-pushed the lambdas-var branch from c89769b to 078fdcd Compare July 27, 2021 05:25

cston marked this pull request as ready for review July 27, 2021 05:28

cston requested review from a team as code owners July 27, 2021 05:28

jcouv reviewed Jul 27, 2021

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jcouv self-assigned this Jul 27, 2021

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a884c74

jcouv approved these changes Jul 27, 2021

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cston mentioned this pull request Jul 27, 2021

Support lambdas and method groups as implicitly-typed variables in tuples and deconstruction #55139

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333fred reviewed Jul 27, 2021

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333fred approved these changes Jul 27, 2021

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cston merged commit 5840335 into dotnet:main Jul 27, 2021

ghost added this to the Next milestone Jul 27, 2021

cston deleted the lambdas-var branch July 27, 2021 18:26

cston modified the milestones: Next, 17.0.P3 Jul 27, 2021

cston added the Feature - Lambda Improvements label Dec 17, 2021

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