In ), variance means the capability to substitute a type with a more derived type or les

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

In object-oriented programming, objects can be composed to build more complex object. Similarly, in functional programming. functions can be composed to build more complex function.

is a function accepting one or more function parameters as input, or returning a function as output. The other functions are

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

Besides named function represented by method members, C# also supports anonymous functions, represented by anonymous method or lambda expression with no name at design time. This part discussed lambda

In C#, functions are represented by methods of types, and other function members of types. In C#, just like just objects have types, methods/functions have types too, which are represented by delegate

In C#, by default, arguments are passed to parameters by value. In the following example, the PassByValue function has a Uri parameter and a int type parameter. Uri is class so it is reference type, a