private static Conversion ToConversion(OverloadResolutionResult <MethodSymbol> result, MethodGroup methodGroup, NamedTypeSymbol delegateType) { // 6.6 An implicit conversion (6.1) exists from a method group (7.1) to a compatible // delegate type. Given a delegate type D and an expression E that is classified as // a method group, an implicit conversion exists from E to D if E contains at least // one method that is applicable in its normal form (7.5.3.1) to an argument list // constructed by use of the parameter types and modifiers of D... // SPEC VIOLATION: Unfortunately, we cannot exactly implement the specification for // the scenario in which an extension method that extends a value type is converted // to a delegate. The code we generate that captures a delegate to a static method // that is "partially evaluated" with the bound-to-the-delegate first argument // requires that the first argument be of reference type. // SPEC VIOLATION: Similarly, we cannot capture a method of Nullable<T>, because // boxing a Nullable<T> gives a T, not a boxed Nullable<T>. (We can capture methods // of object on a nullable receiver, but not GetValueOrDefault.) if (!result.Succeeded) { return(Conversion.NoConversion); } MethodSymbol method = result.BestResult.Member; if (methodGroup.IsExtensionMethodGroup && !method.Parameters[0].Type.IsReferenceType) { return(Conversion.NoConversion); } //cannot capture stack-only types. if (!method.IsStatic && methodGroup.Receiver?.Type?.IsRestrictedType() == true) { return(Conversion.NoConversion); } if (method.ContainingType.IsNullableType() && !method.IsOverride) { return(Conversion.NoConversion); } // NOTE: Section 6.6 will be slightly updated: // // - The candidate methods considered are only those methods that are applicable in their // normal form (§7.5.3.1), and do not omit any optional parameters. Thus, candidate methods // are ignored if they are applicable only in their expanded form, or if one or more of their // optional parameters do not have a corresponding parameter in the targeted delegate type. // // Therefore, we shouldn't get here unless the parameter count matches. // NOTE: Delegate type compatibility is important, but is not part of the existence check. Debug.Assert(method.ParameterCount == delegateType.DelegateInvokeMethod.ParameterCount + (methodGroup.IsExtensionMethodGroup ? 1 : 0)); return(new Conversion(ConversionKind.MethodGroup, method, methodGroup.IsExtensionMethodGroup)); }