C# BoundExpression.AsImmutable方法代码示例

        /// <summary>
        /// If the extension method is applicable based on the "this" argument type, return
        /// the method constructed with the inferred type arguments. If the method is not an
        /// unconstructed generic method, type inference is skipped. If the method is not
        /// applicable, or if constraints when inferring type parameters from the "this" type
        /// are not satisfied, the return value is null.
        /// </summary>
        public static MethodSymbol InferExtensionMethodTypeArguments(this MethodSymbol method, TypeSymbol thisType, Compilation compilation, ref HashSet<DiagnosticInfo> useSiteDiagnostics)
        {
            Debug.Assert(method.IsExtensionMethod);
            Debug.Assert((object)thisType != null);

            if (!method.IsGenericMethod || method != method.ConstructedFrom)
            {
                return method;
            }

            // We never resolve extension methods on a dynamic receiver.
            if (thisType.IsDynamic())
            {
                return null;
            }

            var containingAssembly = method.ContainingAssembly;
            var errorNamespace = containingAssembly.GlobalNamespace;
            var conversions = new TypeConversions(containingAssembly.CorLibrary);

            // There is absolutely no plausible syntax/tree that we could use for these
            // synthesized literals.  We could be speculatively binding a call to a PE method.
            var syntaxTree = CSharpSyntaxTree.Dummy;
            var syntax = (CSharpSyntaxNode)syntaxTree.GetRoot();

            // Create an argument value for the "this" argument of specific type,
            // and pass the same bad argument value for all other arguments.
            var thisArgumentValue = new BoundLiteral(syntax, ConstantValue.Bad, thisType) { WasCompilerGenerated = true };
            var otherArgumentType = new ExtendedErrorTypeSymbol(errorNamespace, name: string.Empty, arity: 0, errorInfo: null, unreported: false);
            var otherArgumentValue = new BoundLiteral(syntax, ConstantValue.Bad, otherArgumentType) { WasCompilerGenerated = true };

            var paramCount = method.ParameterCount;
            var arguments = new BoundExpression[paramCount];
            for (int i = 0; i < paramCount; i++)
            {
                var argument = (i == 0) ? thisArgumentValue : otherArgumentValue;
                arguments[i] = argument;
            }

            var typeArgs = MethodTypeInferrer.InferTypeArgumentsFromFirstArgument(
                conversions,
                method,
                arguments.AsImmutable(),
                ref useSiteDiagnostics);

            if (typeArgs.IsDefault)
            {
                return null;
            }

            int firstNullInTypeArgs = -1;

            // For the purpose of constraint checks we use error type symbol in place of type arguments that we couldn't infer from the first argument.
            // This prevents constraint checking from failing for corresponding type parameters. 
            var notInferredTypeParameters = PooledHashSet<TypeParameterSymbol>.GetInstance();
            var typeParams = method.TypeParameters;
            var typeArgsForConstraintsCheck = typeArgs;
            for (int i = 0; i < typeArgsForConstraintsCheck.Length; i++)
            {
                if ((object)typeArgsForConstraintsCheck[i] == null)
                {
                    firstNullInTypeArgs = i;
                    var builder = ArrayBuilder<TypeSymbol>.GetInstance();
                    builder.AddRange(typeArgs, firstNullInTypeArgs);

                    for (; i < typeArgsForConstraintsCheck.Length; i++)
                    {
                        var typeArg = typeArgsForConstraintsCheck[i];
                        if ((object)typeArg == null)
                        {
                            notInferredTypeParameters.Add(typeParams[i]);
                            builder.Add(ErrorTypeSymbol.UnknownResultType);
                        }
                        else
                        {
                            builder.Add(typeArg);
                        }
                    }

                    typeArgsForConstraintsCheck = builder.ToImmutableAndFree();
                    break;
                }
            }

            // Check constraints.
            var diagnosticsBuilder = ArrayBuilder<TypeParameterDiagnosticInfo>.GetInstance();
            var substitution = new TypeMap(typeParams, typeArgsForConstraintsCheck.SelectAsArray(TypeMap.TypeSymbolAsTypeWithModifiers));
            ArrayBuilder<TypeParameterDiagnosticInfo> useSiteDiagnosticsBuilder = null;
            var success = method.CheckConstraints(conversions, substitution, typeParams, typeArgsForConstraintsCheck, compilation, diagnosticsBuilder, ref useSiteDiagnosticsBuilder, 
                                                  ignoreTypeConstraintsDependentOnTypeParametersOpt: notInferredTypeParameters.Count > 0 ? notInferredTypeParameters : null);
            diagnosticsBuilder.Free();
            notInferredTypeParameters.Free();

//.........这里部分代码省略.........