tmp/tmp8r7i36m4/{from.md → to.md}
RENAMED
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| 1 |
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#### General <a id="class.ctor.general">[[class.ctor.general]]</a>
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A *declarator* declares a *constructor* if it is a function declarator
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[[dcl.fct]] of the form
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``` bnf
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ptr-declarator '(' parameter-declaration-clause ')' noexcept-specifierₒₚₜ attribute-specifier-seqₒₚₜ
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```
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where the *ptr-declarator* consists solely of an *id-expression*, an
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optional *attribute-specifier-seq*, and optional surrounding
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parentheses, and the *id-expression* has one of the following forms:
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- in a friend declaration [[class.friend]], the *id-expression* is a
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*qualified-id* that names a constructor [[class.qual]];
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- otherwise, in a *member-declaration* that belongs to the
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*member-specification* of a class or class template, the
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*id-expression* is the injected-class-name [[class.pre]] of the
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immediately-enclosing entity;
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- otherwise, the *id-expression* is a *qualified-id* whose
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*unqualified-id* is the injected-class-name of its lookup context.
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Constructors do not have names. In a constructor declaration, each
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*decl-specifier* in the optional *decl-specifier-seq* shall be `friend`,
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`inline`, `constexpr`, `consteval`, or an *explicit-specifier*.
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[*Example 1*:
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``` cpp
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struct S {
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S(); // declares the constructor
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};
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S::S() { } // defines the constructor
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```
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— *end example*]
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A constructor is used to initialize objects of its class type.
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[*Note 1*: Because constructors do not have names, they are never found
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during unqualified name lookup; however an explicit type conversion
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using the functional notation [[expr.type.conv]] will cause a
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constructor to be called to initialize an object. The syntax looks like
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an explicit call of the constructor. — *end note*]
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[*Example 2*:
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``` cpp
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complex zz = complex(1,2.3);
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cprint( complex(7.8,1.2) );
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```
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— *end example*]
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[*Note 2*: For initialization of objects of class type see
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[[class.init]]. — *end note*]
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An object created in this way is unnamed.
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[*Note 3*: [[class.temporary]] describes the lifetime of temporary
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objects. — *end note*]
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[*Note 4*: Explicit constructor calls do not yield lvalues, see
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[[basic.lval]]. — *end note*]
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[*Note 5*: Some language constructs have special semantics when used
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during construction; see [[class.base.init]] and
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[[class.cdtor]]. — *end note*]
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A constructor can be invoked for a `const`, `volatile` or `const`
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`volatile` object. `const` and `volatile` semantics [[dcl.type.cv]] are
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not applied on an object under construction. They come into effect when
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the constructor for the most derived object [[intro.object]] ends.
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The address of a constructor shall not be taken.
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[*Note 6*: A `return` statement in the body of a constructor cannot
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specify a return value [[stmt.return]]. — *end note*]
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A constructor shall not be a coroutine.
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A constructor shall not have an explicit object parameter [[dcl.fct]].
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