Lambda表达式通用语法 [英] Lambda expression common syntax

问题描述

我可以遵循任何简单的synax或规则在C#中构建"lambda表达式"吗?我读了一些文章并了解了lambda表达式是什么，但是如果我有通用的语法或规则会有所帮助.

Can I follow any simple synax or rules for building "lambda expression" in C#? I read some articles and understood what a lambda expression is, but if I have the general syntax or rules that would be helpful.

推荐答案

根据具体情况，有多种表达lambda的方法-一些示例:

There are multiple ways of expressing lambdas, depending on the exact scenario - some examples:

    // simplest form; no types, no brackets
    Func<int, int> f1 = x => 2 * x;
    // optional exlicit argument brackets
    Func<int, int> f2 = (x) => 2 * x;
    // optional type specification when used with brackets
    Func<int, int> f3 = (int x) => 2 * x;
    // multiple arguments require brackets (types optional)
    Func<int, int, int> f4 = (x, y) => x * y;
    // multiple argument with explicit types
    Func<int, int, int> f5 = (int x, int y) => x * y;

lambda的签名必须与所使用的委托的签名匹配(无论是显式的，如上面的那样，还是由上下文暗示的，例如.Select(cust => cust.Name)

The signature of the lambda must match the signature of the delegate used (whether it is explicit, like above, or implied by the context in things like .Select(cust => cust.Name)

您可以通过使用一个空的表达式列表来使用不带参数的lambdas :

You can use lambdas without arguments by using an empty expression list:

    // no arguments
    Func<int> f0 = () => 12;

理想情况下，右侧的表达正是这样；单个表达式.编译器可以将其转换为 delegate 或 Expression树:

Ideally, the expression on the right hand side is exactly that; a single expression. The compiler can convert this to either a delegate or an Expression tree:

    // expression tree
    Expression<Func<int, int, int>> f6 = (x, y) => x * y;

但是；您也可以使用语句块，但这只能用作delegate:

However; you can also use statement blocks, but this is then only usable as a delegate:

    // braces for a statement body
    Func<int, int, int> f7 = (x, y) => {
        int z = x * y;
        Console.WriteLine(z);
        return z;
    };

请注意，即使.NET 4.0 Expression树支持语句主体，但C#4.0编译器不会为您执行此操作，因此除非另有说明，否则您仅限于简单的Expression树您以艰难的方式"做到；有关更多信息，请参见我在InfoQ上的文章.

Note that even though the .NET 4.0 Expression trees support statement bodies, the C# 4.0 compiler doesn't do this for you, so you are still limited to simple Expression trees unless you do it "the hard way"; see my article on InfoQ for more information.

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