我正在试验 nameof 和泛型。我没有得到预期的结果。我不确定这是否是规范的一部分。

class MainClass
{
    public static void Main (string[] args)
    {
        Console.WriteLine ($"Hello { nameof(FooBar<string>)! }");
    }
}

class FooBar<T> { }

我得到的输出是

Hello FooBar!

我希望有一些关于类型参数的细节。

我尝试了一种方法，但由于编译器错误而失败:

class MainClass
{
    public static void Main (string[] args)
    {
        Console.WriteLine ($"Hello { nameof(Do<string>) }");
    }

    public static T Do<T>() {}
}

Error CS8084: An argument to nameof operator cannot be method group with type arguments (CS8084) (foo)

这是因为 nameof 是一个编译时构造，而泛型是在运行时初始化的类型吗？还是有其他限制？

最佳答案

I would expect some details about the type parameters

来自设计文档:

Result of nameof. The result of nameof depends on the symbols that its argument bound to:

One or more members: if all members have the same metadata name then the result of nameof is that name; otherwise it is an error "This argument refers to multiple elements with different names". The metadata name of a member IorI< isA1...AK>` is simply "I" after standard identifier transformations have been applied.

<T>由于不允许 <> 的标准标识符转换(C# 规范中的第 2.4.2 节)，参数被删除作为有效标识符。首先删除任何前导 @，然后转换 Unicode 转义序列，然后删除所有格式字符。这当然仍然发生在编译时。当您尝试打印泛型类型的名称时，您也可以看到这一点:

typeof(List<string>).Name;

将导致:

List`1

Is this because nameof is a compile-time construct and generics are types initialized at runtime? Or is there some other limitation?

第二个错误在设计上被指定为无效，以避免 nameof 中的重载解析复杂化。 :

Allow generic type arguments? Presumably 'yes' when naming a type since that's how expression binding already works. And presumably 'no.' when naming a method-group since type arguments are used/inferred during overload resolution, and it would be confusing also to have to deal with that in nameof.

我们可以在 roslyn 代码库中清楚地看到:

private BoundExpression BindNameofOperatorInternal(InvocationExpressionSyntax node, 
                                                   DiagnosticBag diagnostics)
{
    CheckFeatureAvailability(node.GetLocation(), MessageID.IDS_FeatureNameof, diagnostics);

    var argument = node.ArgumentList.Arguments[0].Expression;
    string name = "";

    // We relax the instance-vs-static requirement for top-level member access expressions by creating a NameofBinder binder.
    var nameofBinder = new NameofBinder(argument, this);
    var boundArgument = nameofBinder.BindExpression(argument, diagnostics);

    if (!boundArgument.HasAnyErrors && CheckSyntaxForNameofArgument(argument, out name, diagnostics) && boundArgument.Kind == BoundKind.MethodGroup)
    {
        var methodGroup = (BoundMethodGroup)boundArgument;
        if (!methodGroup.TypeArgumentsOpt.IsDefaultOrEmpty)
        {
            // method group with type parameters not allowed
            diagnostics.Add(ErrorCode.ERR_NameofMethodGroupWithTypeParameters, argument.Location);
        }
        else
        {
            nameofBinder.EnsureNameofExpressionSymbols(methodGroup, diagnostics);
        }
    }

    return new BoundNameOfOperator(node, boundArgument, ConstantValue.Create(name), Compilation.GetSpecialType(SpecialType.System_String));
}

有关完整规范，请参阅:https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/expressions

关于c# - nameof 与泛型，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29878137/