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I don't really get lambda expressions. While they've been around since the days of ALGOL, I didn't start hearing about them until fairly recently, when Python and Ruby became very popular. Now that C# has the => syntax, people in my world (.NET) are talking about lamdba expressions more and more.
I've read the Wikipedia article on the lambda calculus, but I'm not really a math guy. I don't really understand it from a practical perspective. When would I use lambda expressions? Why? How would I know that it's what I should be doing?
Can you show examples of how you would solve problems with lambda expressions, in a before-and-after format? Any imperative language is fine, but C# would be easiest for me to understand.
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Fortunately, you can assign lambda expressions to variables and reuse them, as you would with objects.
Let us look at the new JDK 8 lambda expressions and Stream api's distinct() method to remove duplicates. distinct() method internally calls equals() method on each value and filters the duplicates objects. In our example, we are adding Strings to the list so equals() method of String class will be called.
A lambda function is a small anonymous function. A lambda function can take any number of arguments, but can only have one expression.
The body of a statement lambda can consist of any number of statements; however, in practice there are typically no more than two or three.
Basically as far as C# is concerned, lambda expressions are an easy way to create a delegate (or an expression tree, but let's leave those aside for now).
In C# 1 we could only create delegate instances from normal methods. In C# 2 we gained anonymous methods. In C# 3 we gained lambda expressions, which are like more concise anonymous methods.
They're particularly concise when you want to express some logic which takes one value and returns a value. For instance, in the context of LINQ:
// Only include children - a predicate var query = dataSource.Where(person => person.Age < 18) // Transform to sequence of names - a projection .Select(person => person.Name); There's a fuller discussion of this - along with other aspects - in my article on closures.
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