c# - Lambda 表达式语法糖？

Question

我刚刚遇到以下代码（.NET 3.5），它看起来不应该编译给我，但它确实，并且工作正常：

bool b = selectedTables.Any(table1.IsChildOf));

Table.IsChildOf 实际上是一个具有以下签名的方法：

public bool IsChildOf(Table otherTable)

我认为这相当于：

bool b = selectedTables.Any(a => table1.IsChildOf(a));

如果是这样，正确的术语是什么？

Answer 1

This is a method group conversion, and it's been available since C# 2. As a simpler example, consider:

public void Foo()
{
}

...

ThreadStart x = Foo;
ThreadStart y = new ThreadStart(Foo); // Equivalent code

Note that this is not quite the same as the lambda expression version, which will capture the variable table1, and generate a new class with a method in which just calls IsChildOf. For Any that isn't important, but the difference would be important for Where:

var usingMethodGroup = selectedTables.Where(table1.IsChildOf);
var usingLambda = selectedTables.Where(x => table1.IsChildOf(x));
table1 = null;

// Fine: the *value* of `table1` was used to create the delegate
Console.WriteLine(usingMethodGroup.Count());

// Bang! The lambda expression will try to call IsChildOf on a null reference
Console.WriteLine(usingLambda.Count());

Answer 2

该表达式table1.IsChildOf称为方法组。

你是对的，它是等价的，这确实是句法糖。

Answer 3

它被称为方法组。Resharper 鼓励这种代码。