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CWG2871 [class.default.ctor] p1 should cover the constructor template  #510

Closed
cplusplus/draft
#7099
Closed
CWG2871 [class.default.ctor] p1 should cover the constructor template #510
cplusplus/draft
#7099

Description

@xmh0511
xmh0511
opened on Mar 5, 2024

Full name of submitter (unless configured in github; will be published with the issue): Jim X

[class.default.ctor] p1 says:

If there is no user-declared constructor for class X, a non-explicit constructor having no parameters is implicitly declared as defaulted ([dcl.fct.def]).

Consider this example:

struct X{
  template<class U> X(U){} // #2
};
int main(){
   X x;  // #1
}

#1 is ill-formed since no matching function for call to 'X::X()'. [class.default.ctor] p1 should cover this example, however, #2 is a user-declared constructor template, and the implicitly instantiated declaration is not user-declared anyway.

Suggested Resolution

If there is no user-declared constructor or constructor template for class X, a non-explicit constructor having no parameters is implicitly declared as defaulted ([dcl.fct.def]).

Activity

  1. jensmaurer
    changed the title [-][class.default.ctor] p1 should cover the constructor template [/-] [+]CWG2871 [class.default.ctor] p1 should cover the constructor template [/+] on Mar 17, 2024

  2. jensmaurer commented on Mar 17, 2024

    @jensmaurer
    jensmaurer
    on Mar 17, 2024
    Member

    CWG2871

  3. lprv commented on Apr 6, 2024

    @lprv
    lprv
    on Apr 6, 2024

    There are plenty of other uses of the undecorated term 'constructor' in the standard that are clearly meant to include templates: [basic.scope.scope]/4, [dcl.init.aggr]/1.1, [namespace.udecl]/2 and /13, [class.mem.general]/22, various subclauses of [over.match.funcs], etc. Why is it a problem in this particular case?

  4. frederick-vs-ja commented on Apr 8, 2024

    @frederick-vs-ja
    frederick-vs-ja
    on Apr 8, 2024

    There are plenty of other uses of the undecorated term 'constructor' in the standard that are clearly meant to include templates: [basic.scope.scope]/4, [dcl.init.aggr]/1.1, [namespace.udecl]/2 and /13, [class.mem.general]/22, various subclauses of [over.match.funcs], etc. Why is it a problem in this particular case?

    Most are about inheriting constructors. I think there should be a concentrated issue on this.

  5. jensmaurer
    closed this as completedon Jul 15, 2024
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