As fore mentioned, LINQ to Objects standard query methods (also called standard query operators) are provided as static methods of System.Linq.Enumerable type, most of which are IEnumerable<T> extensi

LINQ to Objects queries .NET objects in local memory of current application or service. Its data source and the queries are represented by IEnumerable<T> interface, and it is executed sequentially. Th

Pattern matching is a common feature in functional languages. C# 7.0 introduces basic pattern matching in is expression and switch statement, including constant value as pattern and type as pattern, a

Immutability is an important aspect of functional programming. As discussed in the introduction chapter, imperative/object-oriented programming is usually mutable and stateful, and functional programm

The previous chapter discusses that functional programming encourages modelling data as immutable. Functional programming also encourages modelling operations as pure functions. The encouraged purity

In programming languages with subtyping support, variance is the ability to substitute a type with a different subtype or supertype in a context. For example, having a subtype and a supertype, can a f

C# 3.0 introduces query expression, a SQL-like query syntactic sugar for query methods composition.

As demonstrated in the introduction chapter, in object-oriented programming, program is modelled as objects, and object composition is very common, which combines simple objects to more complex object

The delegate chapter and other previous chapters have demonstrated that in C#, function supports many operations that are available for object. This chapter discusses one more aspect, higher-order fun

C# lambda expression is a powerful syntactic sugar. Besides representing anonymous function, the same syntax can also represent expression tree. An expression tree is an immutable tree data structure