Predicates

I love predicates. They are a rather recent addition to my toolkit, but already I use them every time I can. What is a predicate you ask?

A predicate is a piece of logic to affirm or deny the subject of a proposition. Programmatically, a predicate is a function that returns true or false when given a class or value. For example.

public bool Contains(IProduct product)

{

    Func<IProduct, bool> predicate = x => x.Name == product.Name;

    foreach (var item in products)

    {

        if (predicate(item))

        {

            return true;

        }

    }

    return false;

}

Pretty cool, but let’s get rid of that foreach.

public bool Contains(IProduct product)

{

    Func<IProduct, bool> predicate = x => x.Name == product.Name;

    return products.FirstOrDefault(predicate) != null;

}

And finally…

public bool Contains(IProduct product)

{

    return products.FirstOrDefault(x => x.Name == product.Name) != null;

}

We can also filter lists in a similar fashion using Where

public IEnumerable<IProduct> FindByName(IProduct product)

{

    return products.Where(x => x.Name == product.Name);

}

Update: Thanks to Conrad for helping me improve this and remove the need for an Extension Method.