为什么要重载true和false而不是定义bool运算符? [英] Why overload true and false instead of defining bool operator?

问题描述

我一直在阅读有关C#中对true和false进行重载的信息，我想我了解这与定义bool运算符之间的基本区别.我周围看到的示例是这样的:

public static bool operator true(Foo foo) {
  return (foo.PropA > 0);
}
public static bool operator false(Foo foo) {
  return (foo.PropA <= 0);
}

对我来说，这等于说:

public static implicit operator bool(Foo foo) {
  return (foo.PropA > 0);
}

据我所知，区别在于，通过分别定义true和false，您可以拥有一个既是true还是false的对象，或者不是true也不是false的对象:

public static bool operator true(Foo foo) { return true; }
public static bool operator false(Foo foo) { return true; }
//or
public static bool operator true(Foo foo) { return false; }
public static bool operator false(Foo foo) { return false; }

我确定允许这样做是有原因的，但我只是想不出它是什么.对我来说，如果您希望将一个对象转换为true或false，那么一个布尔运算符最有意义.

任何人都可以给我一种以其他方式有意义的方案吗?

谢谢

解决方案

为文档说，重载true和false旨在支持(可为空)数据库类型(是/否，是/否，0/1等).

当然，与任何运算符一样，它们的定义也可能不一致.您有责任退还明智的东西.编译器只需要一个或两个都不需要.

I've been reading about overloading true and false in C#, and I think I understand the basic difference between this and defining a bool operator. The example I see around is something like:

public static bool operator true(Foo foo) {
  return (foo.PropA > 0);
}
public static bool operator false(Foo foo) {
  return (foo.PropA <= 0);
}

To me, this is the same as saying:

public static implicit operator bool(Foo foo) {
  return (foo.PropA > 0);
}

The difference, as far as I can tell, is that by defining true and false separately, you can have an object that is both true and false, or neither true nor false:

public static bool operator true(Foo foo) { return true; }
public static bool operator false(Foo foo) { return true; }
//or
public static bool operator true(Foo foo) { return false; }
public static bool operator false(Foo foo) { return false; }

I'm sure there's a reason this is allowed, but I just can't think of what it is. To me, if you want an object to be able to be converted to true or false, a single bool operator makes the most sense.

Can anyone give me a scenario where it makes sense to do it the other way?

Thanks

解决方案

As the docs say, overloading true and false is intended to support (nullable) database-types (Yes/No, Y/N, 0/1, etc).

And of course you can define them inconsistently, as with any operator. It is your responsibility to return something sensible. The compiler goes no further than requiring neither or both.

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