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-modifier

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 (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 formal-parameter-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 constructor-initializers.

In This Section:

• 17.10.1: Constructor initializers
• 17.10.2: Instance variable initializers
• 17.10.3: Constructor execution
• 17.10.4: Default constructors
• 17.10.5: Private constructors
• 17.10.6: Optional instance constructor parameters