C# 3.0 Pocket Reference, 2nd Edition

Lambda Expressions (C# 3.0)

A lambda expression is an unnamed method written in place of a delegate instance. The compiler immediately converts the lambda expression to either:

• A delegate instance.

• An expression tree, of type Expression<TDelegate>, representing the code inside the lambda expression in a traversable object model. This allows the lambda expression to be interpreted later at runtime (we describe the process in Chapter 8 of C# 3.0 in a Nutshell).

Given the following delegate type:

	delegate int Transformer (int i);

we could assign and invoke the lambda expression x => x * x as follows:

	Transformer sqr = x => x * x;
	Console.WriteLine (sqr(3));    // 9

Note

Internally, the compiler resolves lambda expressions of this type by writing a private method and moving the expression’s code into that method.

A lambda expression has the following form:

        (parameters) => expression-or-statement-block

For convenience, you can omit the parentheses if and only if there is exactly one parameter of an inferable type.

In our example, there is a single parameter, x, and the expression is x*x:

	x => x * x;

Each parameter of the lambda expression corresponds to a delegate parameter, and the type of the expression (which may be void) corresponds to the return type of the delegate.

In our example, x corresponds to parameter i, and the expression x * x corresponds to the return type int, therefore being compatible with the Transformer delegate:

	delegate int Transformer (int i);

A lambda expression’s code can ...