recursive-patterns(19) Distinguish irrefutable and refutable patterns in the is expression
#26035
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Both refutable and irrefutable is-pattern matches affect definite assignment: - an irrefutable match leaves pattern variables definitely assigned - a refutable match is an error Fixes dotnet#25890 Also, we check to see if a constant input makes the result refutable or irrefutable: - If a constant cannot match the pattern, we issue a warning - If a constant always matches a constant pattern, we issue a warning The latter two are subject to compat council approval. Fixes dotnet#16099
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is expressionis expression
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| operand = BadExpression(node, operand).MakeCompilerGenerated(); |
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Why are we doing this unconditionally now? #ByDesign
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Because it is unconditionally illegal to have a lambda or method group here. This line just gives the expression an error type so later code doesn't see a typeless expression.
In reply to: 180249518 [](ancestors = 180249518)
| if (!reachableLabels.Contains(node.WhenTrueLabel)) | ||
| { | ||
| SetState(this.StateWhenFalse); | ||
| SetConditionalState(UnreachableState(), this.State); |
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If SetConditionalState zeroes out the current state, what's the point of calling SetState before this? #Resolved
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The call to UnreachableState() requires as a precondition that the current state is not a split state.
In reply to: 180252872 [](ancestors = 180252872)
| else if (!reachableLabels.Contains(node.WhenFalseLabel)) | ||
| { | ||
| SetState(this.StateWhenTrue); | ||
| SetConditionalState(this.State, UnreachableState()); |
| @@ -212,9 +212,6 @@ public static void Main() | |||
| // (10,13): error CS8117: Invalid operand for pattern match; value required, but found '<null>'. | |||
| // if (null is dynamic t) { } // null not allowed | |||
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Looks like this text is out of date. #Resolved
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| { | ||
| diagnostics.Add(ErrorCode.WRN_GivenExpressionNeverMatchesPattern, node.Location); | ||
| } | ||
| else if (!decisionDag.ReachableLabels.Contains(whenFalseLabel) && pattern.Kind == BoundKind.ConstantPattern) |
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&& pattern.Kind == BoundKind.ConstantPattern [](start = 83, length = 44)
When is the pattern not a ConstantPattern? #Resolved
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const string s = null;
System.Console.WriteLine(s is string { Length: 3 });#Resolved
Both refutable and irrefutable is-pattern matches affect definite assignment:
Fixes Add tests for irrefutable patterns #25890
Also, we check to see if a constant input makes the result refutable or irrefutable:
The latter two are subject to compat council approval.
Fixes No warning for identity pattern-matching comparison #16099