有没有什么办法来否定一个predicate？ [英] Is there any way to negate a Predicate?

问题描述

我想做的事情是这样的：

I want to do something like this:

List<SomeClass> list1 = ...
List<SomeClass> list2 = ...
Predicate<SomeClass> condition = ...

...

list2.RemoveAll (!condition);

...

list2.AddRange (list1.FindAll (condition));

不过，这将导致一个编译器错误，因为 不能适用于 predicate＆LT;！SomeClass的＆GT; 。有没有办法做到这一点？

However, this results in a compiler error, as ! can't be applied to Predicate<SomeClass>. Is there any way to do this?

推荐答案

您可以使用lambda EX pression定义一个匿名委托就地是否定的predicate结果的结果：

You could use a lambda expression to define an anonymous delegate inplace that is the result of negating the result of the predicate:

list.RemoveAll(x => !condition(x));    

另一种选择：

Another option:

static Predicate<T> Negate<T>(Predicate<T> predicate) {
     return x => !predicate(x);
}

用法：

// list is List<T> some T
// predicate is Predicate<T> some T
list.RemoveAll(Negate(predicate));

这是 list.RemoveAll（！条件）不工作的原因是没有定义！运营商与会代表。这就是为什么你必须在条件如上图所示。

The reason that list.RemoveAll(!condition) does not work is that there is no ! operator defined on delegates. This is why you must define a new delegate in terms of condition as shown above.

这篇关于有没有什么办法来否定一个predicate？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！