17.10 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:
attributesopt constructor-modifiersopt constructor-declarator
constructor-body
constructor-modifiers:
constructor-modifier
constructor-modifiers constructor-modifier
constructor-modifier:
public
protected
internal
private
extern
constructor-declarator:
identifier ( formal-parameter-listopt ) constructor-initializeropt
constructor-initializer:
: base ( argument-listopt )
: this ( argument-listopt )
constructor-body:
block
;
A constructor-declaration may include a set of attributes (§24), a valid
combination of the four access modifiers
(§17.2.3), and an extern (§17.5.7) 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 formalparameter-
list of a method (§17.5). The formal parameter list defines the signature (
§10.6) of an instance
constructor and governs the process whereby overload resolution (§14.4.2)
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 (§10.5.4).
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 §17.10.1.
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 (§17.5.8).
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 (§17.10.4).
Instance constructors are invoked by object-creation-expressions (§14.5.10.1
) and through constructorinitializers.