Question

I have recently moved to .net 3.0 (windows forms, C#). I want to know more about predicates and lambda expressions. Where should we use them? Do they improve performance? and how do they work internally. Thanks.

Answer 1

If you search Stack Overflow you’ll find about a thousand answers explaining what they’re for. In short – a lambda is a way of writing an anonymous method at the point where you want to pass it to another method. Technically the same as the delegate syntax for an anonymous method, although with added powers of type inference so you don’t need to state the parameter types. A predicate is a method that accepts some value and returns a bool – an example would be the argument to Where.

A lambda that doesn’t refer to any external variables gets turned into a private static method with a made-up name. If it refers to instance members of the enclosing class, it becomes an instance method. If it refers to local variables, those variables get “hoisted” into being fields of a compiler-generated class that is allocated when the enclosing method starts running, and the lambda’s body becomes a method in that new class.

As for performance, they don’t make that much difference. They involve the creation of temporary objects, but I find that these are collected extremely efficiently by the GC.