C# NamedTypeSymbol.DelegateParameters方法代码示例

        ////////////////////////////////////////////////////////////////////////////////
        //
        // Inferred return type
        //
        private TypeSymbol InferReturnType(BoundExpression source, NamedTypeSymbol target, ref HashSet<DiagnosticInfo> useSiteDiagnostics)
        {
            Debug.Assert((object)target != null);
            Debug.Assert(target.IsDelegateType());
            Debug.Assert((object)target.DelegateInvokeMethod != null && !target.DelegateInvokeMethod.HasUseSiteError,
                         "This method should only be called for legal delegate types.");
            Debug.Assert(!target.DelegateInvokeMethod.ReturnsVoid);

            // We should not be computing the inferred return type unless we are converting
            // to a delegate type where all the input types are fixed.
            Debug.Assert(!HasUnfixedParamInInputType(source, target));

            // Spec 7.5.2.12: Inferred return type:
            // The inferred return type of an anonymous function F is used during
            // type inference and overload resolution. The inferred return type
            // can only be determined for an anonymous function where all parameter
            // types are known, either because they are explicitly given, provided
            // through an anonymous function conversion, or inferred during type
            // inference on an enclosing generic method invocation.
            // The inferred return type is determined as follows:
            // * If the body of F is an expression (that has a type) then the 
            //   inferred return type of F is the type of that expression.
            // * If the body of F is a block and the set of expressions in the
            //   blocks return statements has a best common type T then the
            //   inferred return type of F is T.
            // * Otherwise, a return type cannot be inferred for F.

            if (source.Kind != BoundKind.UnboundLambda)
            {
                return null;
            }

            var anonymousFunction = (UnboundLambda)source;
            if (anonymousFunction.HasSignature)
            {
                // Optimization: 
                // We know that the anonymous function has a parameter list. If it does not
                // have the same arity as the delegate, then it cannot possibly be applicable.
                // Rather than have type inference fail, we will simply not make a return
                // type inference and have type inference continue on.  Either inference
                // will fail, or we will infer a nonapplicable method. Either way, there
                // is no change to the semantics of overload resolution.

                var originalDelegateParameters = target.DelegateParameters();
                if (originalDelegateParameters.IsDefault)
                {
                    return null;
                }

                if (originalDelegateParameters.Length != anonymousFunction.ParameterCount)
                {
                    return null;
                }
            }

            var fixedDelegate = GetFixedDelegate(target);
            var fixedDelegateParameters = fixedDelegate.DelegateParameters();
            // Optimization:
            // Similarly, if we have an entirely fixed delegate and an explicitly typed
            // anonymous function, then the parameter types had better be identical.
            // If not, applicability will eventually fail, so there is no semantic
            // difference caused by failing to make a return type inference.
            if (anonymousFunction.HasExplicitlyTypedParameterList)
            {
                for (int p = 0; p < anonymousFunction.ParameterCount; ++p)
                {
                    if (anonymousFunction.ParameterType(p) != fixedDelegateParameters[p].Type)
                    {
                        return null;
                    }
                }
            }

            // Future optimization: We could return null if the delegate has out or ref parameters
            // and the anonymous function is an implicitly typed lambda. It will not be applicable.

            // We have an entirely fixed delegate parameter list, which is of the same arity as
            // the anonymous function parameter list, and possibly exactly the same types if
            // the anonymous function is explicitly typed.  Make an inference from the
            // delegate parameters to the return type.

            return anonymousFunction.InferReturnType(fixedDelegate, ref useSiteDiagnostics);
        }