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Dan Donahue

Musician. Traveler. Programmer.

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This post is part of a series:

In my last post, I explained how to use anonymous methods, or inline delegates, to remove a bunch of unnecessary code from your class. This post is going to explain how lambda expressions are really just a syntatic helper to aid in the removal of more 'extra' code and to make anonymous methods a little more readable.

And that's really what lambda expressions are - cleaner ways to write anonymous methods/inline delegates.

Let's look at our example from last time. To handle two different filtering scenarios, we had this:

This isn't bad, but you still have to use the delegate keyword and declare a function, complete with parentheses and curly braces inline. That can get hard to match up pretty quickly. So here are these same lines using lambda expressions:

As I said earlier, this is really just a cleaner way to write the delegate. The left side of the lambda expression declares the inputs. You will often see these as x. That's just a convention. I chose team because I think it's more descriptive. The right side of the lambda expression holds the statement block, or function body. Pretty simple - lambda expressions are delegates. Nothing to be afraid of.

A few notes about lambda expressions before this post is over.

When a lambda expression's body contains only one line of code, you don't need a return - the result of that line of code is assumed to be the return value. So above, the line evaluates to a boolean, so that is considered the return value. That said - you CAN write lambda expressions containing multiple lines of code, but you then have to include the return keyword and wrap your expression body in curly braces. Here's a quick example:

Not super realistic, it filters by teams whose name is ten characters long.

Also - lambda expressions can take zero parameters. In that case, you use an empty set of parentheses on the left side like this:

And they can also take multiple inputs. For example, if you wanted to compare two teams:

So there you go. Lambda expressions are nothing more than clean ways to write delegates. And delegates are a really powerful and useful feature to allow you to separate a method from its implementation.

There's going to be one more post in this series. It's a bit of a tangent rather than a continuation, but I wanted to introduce a few classes that .NET provides to help facilitate the use of delegates in your code.