Instance constructors

An instance constructor is a member that implements the actions required to initialize an instance of a class. Instance constructors are declared using constructor-declarations:

constructor-declaration:
attributes_opt constructor-modifiers_opt constructor-declarator constructor-body

constructor-modifiers:
constructor-modifier
constructor-modifiers constructor-modifier

constructor-modifier:
public
protected
internal
private
extern

constructor-declarator:
identifier (formal-parameter-list_opt) constructor-initializer_opt

constructor-initializer:
: base (argument-list_opt)
: this (argument-list_opt)

constructor-body:
block
;

A constructor-declaration may include a set of attributes (§17), a valid combination of the four access modifiers (§10.3.5), and an extern (§10.6.7) modifier. A constructor declaration is not permitted to include the same modifier multiple times.

The identifier of a constructor-declarator must name the class in which the instance constructor is declared. If any other name is specified, a compile-time error occurs.

The optional formal-parameter-list of an instance constructor is subject to the same rules as the formal-parameter-list of a method (§10.6). The formal parameter list defines the signature (§3.6) of an instance constructor and governs the process whereby overload resolution (§7.5.2) selects a particular instance constructor in an invocation.

Each of the types referenced in the formal-parameter-list of an instance constructor must be at least as accessible as the constructor itself (§3.5.4).

The optional constructor-initializer specifies another instance constructor to invoke before executing the statements given in the constructor-body of this instance constructor. This is described further in §10.11.1.

When a constructor declaration includes an extern modifier, the constructor is said to be an external constructor. Because an external constructor declaration provides no actual implementation, its constructor-body consists of a semicolon. For all other constructors, the constructor-body consists of a block which specifies the statements to initialize a new instance of the class. This corresponds exactly to the block of an instance method with a void return type (§10.6.10).

Instance constructors are not inherited. Thus, a class has no instance constructors other than those actually declared in the class. If a class contains no instance constructor declarations, a default instance constructor is automatically provided (§10.11.4).

Instance constructors are invoked by object-creation-expressions (§7.6.10.1) and through constructor-initializers.

Дата добавления: 2015-11-16