'int?' 不包含 'TryFormat' 的定义

Question

我很难理解可空值类型在 C#9 中的工作原理。

以下文档来自：

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/nullable-value-types

我可以写（没有编译错误）：

int? a = 10;
a++; // No need for explicit 'a.Value'

但是我不能写（编译错误）：

Span<char> TryFormatOrNull(int? input)
{
    char[] buffer = new char[512];
    if (input == null) return null;
    _ = input.TryFormat(buffer, out _);
    return buffer;
}

我需要写（没有语法糖）：

Span<char> TryFormatOrNull(int? input)
{
    char[] buffer = new char[512];
    if (input == null) return null;
    _ = input.Value.TryFormat(buffer, out _);
    return buffer;
}

我对可空值类型与成员 function/operator 有何误解？

Answer 1

What did I misunderstood with nullable value types vs member function/operator ?

运算符会自动“提升”（即，非可为空值类型的运算符自动可用于相应的可为空值类型）但方法不会。就这些，真的。

查看 section 12.4.8 of the C# standard for details of lifted operators, and 11.6.2 提升的转化率。

Answer 2

这是因为 ++ 是一个预定义的一元运算符，它可以是 "lifted"（而 TryFormat 方法不是）：

The predefined unary and binary operators or any overloaded operators that are supported by a value type T are also supported by the corresponding nullable value type T?. These operators, also known as lifted operators, produce null if one or both operands are null; otherwise, the operator uses the contained values of its operands to calculate the result.

'int?' 不包含 'TryFormat' 的定义

'int?' does not contain a definition for 'TryFormat'

c#

nullable