FUNC主场迎战主场迎战行动predicate [英] Func vs. Action vs. Predicate

问题描述

通过实际例子和它们的使用，有人可以帮我明白了：

1. 当我们需要Func键代表？


2. 当我们需要Action委托？


3. 当我们需要predicates代表？

解决方案

Func键之间的区别和动作是您只需是否要委托返回一个值（使用函数功能）或不（使用动作）。

函数功能可能是最常使用LINQ - 例如在预测：

  list.Select（X =＆GT; x.SomeProperty）
 

或过滤：

  list.Where（X =＆GT; x.SomeValue == someOtherValue）
 

或键选择：

  list.Join（otherList，X =＆GT; x.FirstKey，Y =＆GT; y.SecondKey，...）
 

动作更常用的如的事情列表＆LT; T＆GT; .ForEach ：执行每个给定的动作列表中的项目。我用这往往小于函数功能，虽然我的做的有时会使用的东西无参数的版本，如 Control.BeginInvoke 和 Dispatcher.BeginInvoke 。

predicate 只是一个特殊的套管 Func键＆LT; T，BOOL＆GT; 真的，所有的前出台在函数功能和大多数行动代表来了。我怀疑，如果我们就已经有了函数功能和动作在他们的各种名目， predicate 将不会被引入......虽然它的确实的传授一定的意义的使用委托的，而函数功能和动作用于广泛不同的目的。

predicate 在主要用于名单＆LT; T＆GT; 像方法的FindAll 和 removeall过。

With real examples and their use, can someone please help me understand:

1. When do we need Func delegate?
2. When do we need Action delegate?
3. When do we need Predicates delegate?

解决方案

The difference between Func and Action is simply whether you want the delegate to return a value (use Func) or not (use Action).

Func is probably most commonly used in LINQ - for example in projections:

 list.Select(x => x.SomeProperty)

or filtering:

 list.Where(x => x.SomeValue == someOtherValue)

or key selection:

 list.Join(otherList, x => x.FirstKey, y => y.SecondKey, ...)

Action is more commonly used for things like List<T>.ForEach: execute the given action for each item in the list. I use this less often than Func, although I do sometimes use the parameterless version for things like Control.BeginInvoke and Dispatcher.BeginInvoke.

Predicate is just a special cased Func<T, bool> really, introduced before all of the Func and most of the Action delegates came along. I suspect that if we'd already had Func and Action in their various guises, Predicate wouldn't have been introduced... although it does impart a certain meaning to the use of the delegate, whereas Func and Action are used for widely disparate purposes.

Predicate is mostly used in List<T> for methods like FindAll and RemoveAll.

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