Questions tagged [predicate]

A Predicate is a method which represents a set of criteria and decides for a given object if these criteria are fulfilled or not. In computer languages a Predicate is expressed as a function which takes a single object as input parameter and returns a boolean value.

Example of a Predicate in .NET Framework / C#

In the .NET Framework the most general form of a Predicate is represented by a generic delegate:

public delegate bool Predicate<in T>(T obj)

An often used alternative representation is:

public delegate TResult Func<in T, out TResult>(T arg)

where TResult is of type bool.

An example of a concrete instance of such a delegate is a method which decides for a given Product by a special citerion if it is expensive or not:

public bool IsExpensive(Product product)
{
    return product.UnitPrice > 1000;
}

Predicates are often used for defining criteria to filter a subset of data out of a larger set and are often expressed as anonymous methods or by lambda expressions:

IEnumerable<Product> expensiveProducts =
    allProducts.Where(p => p.UnitPrice > 1000);