IEnumerable <T>。包含谓词

Question

I need just to clarify that given collection contains an element.

I can do that via collection.Count(foo => foo.Bar == "Bar") > 0) but it will do the unnecessary job - iterate the whole collection while I need to stop on the first occurrence.

But I want to try to use Contains() with a predicate, eg foo => foo.Bar == "Bar" .

Currently IEnumerable<T>.Contains has two signatures:

• IEnumerable<T>.Contains(T)

• IEnumerable<T>.Contains(T, IEqualityComparer<T>)

So I have to specify some variable to check:

var collection = new List<Foo>() { foo, bar };
collection.Contains(foo);

or write my custom IEqualityComparer<Foo> which will be used against my collection:

class FooComparer : IEqualityComparer<Foo>
{
    public bool Equals(Foo f1, Foo f2)
    {
        return (f1.Bar == f2.Bar); // my predicate
    }

    public int GetHashCode(Foo f)
    {
        return f.GetHashCode();
    }   
}

So are there any other methods to use predicate?

Answer 1

.Any(predicate)

sounds like what you want; returns bool , returning true as soon as a match is found, else false . There is also:

.All(predicate)

which behaves in a similar way, returning false as soon as a non-match is found, else true .

Answer 2

You can use Any(predicate) . It will return true or false depending if the predicate exists in a certain collection.

Answer 3

看一下IEnumerable<T>.Any扩展。