Types (class, struct, generic, nullable, tuple)

In scripts we use types to create variables and to call functions.

string s = "text"; //variable s of type string
int k = 5; //variable k of type int
dialog.showInfo(s, k.ToString()); //call function showInfo which is defined in type dialog. Also call function ToString which is defined in type int.

int, string and some other types are built into the C# language; more info in recipe Variables. Many other types are defined in .NET and other libraries, and dialog is an example. More examples:

DateTime dt = DateTime.Now; //variable dt of type DateTime. Also call function Now which is defined in type DateTime.
RECT r = new RECT(1, 2, 3, 4); //variable r of type RECT. Also call a constructor function defined in type RECT.
print.it(dt, r.left); //call function it which is defined in type print. Pass dt and r field left which is defined in type RECT.

There are 5 kinds of types:

  • class. Also known as reference type. Can contain data fields (variables, constants), functions (methods, properties, etc), events and inner types.
  • struct. Also known as value type. Same as class, but variables are stored differently: the value is directly in the variable. A class variable is a reference (pointer) to its value that is stored separately, and the value isn't copied when copying the variable.
  • enum. Defines several integer constants, and nothing else.
  • delegate. Defines a function type (parameters, etc).
  • interface. Defines multiple function types.

You can define new types, with functions etc inside. Example in recipe Functions.

Also C# supports arrays, generic types, nullable value types, tuples, anonymous types and pointers.

Generic types have names like List<T>. They can be used in several ways:

  • Replace T with a type name, like List<string>. Examples in recipe collections.
  • If a parameter is of type T, can be used argument of any supported type.
  • If an out parameter is of type T, argument code can be like out string s.

If a value-type variable is declared like int? i, you can assign it null, which could mean "no value". Often used for optional parameters.

void Func1(bool? b = null) {
	if (b == null) print.it("null");
	else if (b == true) print.it("true");
	else print.it(b.Value);
}

Variables of reference types always can have value null. If a function parameter or return type is like string?, it is just a hint that the function supports null.

Tuples contain several fields (variables) of possibly different types. Often used to returns multiple values from a function, like in the Functions recipe.

(int i, string s) t = (10, "text"); //create a tuple variable t
print.it(t.i, t.s);