C# Linq question

Question

Does LINQ have a sequence operator, which allows to perform some action on every element without projecting it to a new sequence?

This might see a bit awkward, but just for me to know :)

Example:

IEnumerable<IDisposable> x;
x.PERFORM_ACTION_ON_EVERY_ELEMENT(m => m.Dispose());

Obviously, this could be done using something like:

foreach (var element in x) x.Dispose();

But if something actually exists, that would be nice.

Answer 1

No, it doesn't exist. Specifically for the reason you mention: It seems awkward having a single operator that behaves completely different than all the others.

Eric Lippert, one of the C# Compiler developers has an article about this.

But we can go a bit deeper here. I am philosophically opposed to providing such a method, for two reasons.

The first reason is that doing so violates the functional programming principles that all the other sequence operators are based upon. Clearly the sole purpose of a call to this method is to cause side effects.

The purpose of an expression is to compute a value, not to cause a side effect. The purpose of a statement is to cause a side effect. The call site of this thing would look an awful lot like an expression (though, admittedly, since the method is void-returning, the expression could only be used in a “statement expression” context.)

It does not sit well with me to make the one and only sequence operator that is only useful for its side effects.

Answer 2

You can use this method:

public static class Extension
{
    public static IEnumerable<T> ForEach<T>(this IEnumerable<T> source, Action<T> action)
    {
        foreach (var t in source)
        {
            action(t);
        }
        return source;
    }
}

It returns the source so you can pass it along to another extension method as needed. Or if you want to be void, you can change the method a little bit.

Answer 3

The morelinq project has a ForEach operator. LINQ itself doesn't, as LINQ is all about functional programming, and ForEach has side effects.

Answer 4

Here is a similar dicussion on this Run a method on all objects within a collection