C＃3.0 [英] C# 3.0

问题描述

什么是Predicate Deligate。请解释。

What is a "Predicate Deligate". Please explain.

推荐答案

如果通过谓词委托你的意思是一个Predicate< T>，那么这只是表达一个逻辑测试的
a方式（并且是2.0，而不是3.0 - 虽然3.0

可以产生一个谓词来自一个表达式树。


它有签名bool Predicate< T>（T值），意思是给出了

类型的对象T，该方法返回true或false - 对于

过滤器等有用。


此上下文中的委托（实例）一如​​既往地是一个

方法 - 指向这种方法的指针 - 即


public static bool IsEven（int value）{

返回值％ 2 == 0;

}


然后获得委托实例：

Predicate< TisEven = IsEven; //或者，=新谓词< T>（IsEven）在

中手写


然后你可以评价

bool fiveIsEven = isEven（5）;


当然 - 实际上你不会这样做; -p谓词是有用的

当执行表达式的组件时（不是在C＃3.0

意义上......）不可能知道表达本身 - 即List< T>

不能知道我感兴趣的是偶数...


然而，你不需要这个...你可以更简洁;所以，如果我有
有一个List< int>，我可以使用：

List< intevenList = greaterList.FindAll（IsEven）;

或者使用匿名语法：

List< intevenList = greaterList.FindAll（delegate（int value）{return

value％2 == 0;}）;


C＃3.0引入了一个更简单的lambda。表达这一点的方式：


列表< intevenList = greaterList.FindAll（v = v％2 == 0）;


这有用吗任何？

If by "predicate delegate" you mean a Predicate<T>, then this is just
a way of expressing a logical test (and is 2.0, not 3.0 - although 3.0
can produce a predicate from an expression-tree).

It has the signature "bool Predicate<T>(T value)", meaning that given
an object of type T, the method returns true or false - useful for
filters etc.

A delegate (instance) in this context is, as always, an instance of a
method-pointer to such a method - i.e.

public static bool IsEven(int value) {
return value % 2 == 0;
}

then to get a delegate instance:
Predicate<TisEven = IsEven; // or, = new Predicate<T>(IsEven) in
longhand

and then you can evaluate
bool fiveIsEven = isEven(5);

Of course - in reality you wouldn''t do this ;-p Predicates are useful
when the component executing the expression (not in the C#3.0
sense...) cannot possibly know the expression itself - i.e. List<T>
can''t know that I am interested in even numbers...

However, you don''t need this... you can be a lot more terse; so if I
have a List<int>, I can use either:
List<intevenList = biggerList.FindAll(IsEven);
or alternatively using anonymous syntax:
List<intevenList = biggerList.FindAll(delegate (int value) {return
value % 2 == 0;});

C# 3.0 introduces an easier "lambda" way of expressing this:

List<intevenList = biggerList.FindAll(v =v % 2 == 0);

Does that help any?

哎呀：

Predicate< TisEven = IsEven;

应该读过

Predicate< intisEven = IsEven;


Marc

Oops:
Predicate<TisEven = IsEven;
should have read
Predicate<intisEven = IsEven;

Marc

在匿名表达式中或在Lambda表达式中谓词委托？

" RITESHIR" < RI ****** @ discuss.microsoft.com写信息

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Predicate delegate as in anonymous expression or as in Lambda expression?
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什么是Predicate Deligate。请解释。

What is a "Predicate Deligate". Please explain.

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