Question

Lambda expressions seem to be a common stumbling block to those new to .NET. Does anyone have a good resource for explaining them to newbies?

Answer 1

A lambda is simply an anonymous method like this:

delegate(string parm1, int parm2)
{
    // ...
}

The first part of a lambda is for the method parameters. If there are no parameters, or if there are more than one parameter, parentheses are required:

// no parameters
() => null

// one parameter
x => null

// multiple parameters
(x, y, z) => null

A lambda corresponding to the anonymous method above would be written:

(string parm1, int parm2) => ...

Depending on how the lambda is used, the compiler can actually infer the types of the parameters and the return value, so they aren’t always required.

The last part of a lambda is for the method body.

delegate(string parm1, int parm2)
{
    return string.Format("{0}{1}", parm1, parm2);
}

is the same as

(parm1, parm2) =>
{
    return string.Format("{0}{1}", parm1, parm2);
}

If the body of the method is a single line, the lambda does not require a return keyword, nor curly braces:

(parm1, parm2) => string.Format("{0}{1}", parm1, parm2);

Those are the basics. I hope this helps.