c++ - C++11 default class member initialization with initializer list , simultaneously -

can point me please, corresponding paragraph of c++ standard, or maybe can provide explanation why code not compile if uncomment text ({123})?

generally speaking understand wrong usage of default member initialization , initialization via initializer list, can't refer exact reasons.

enum class my: int {     = 1 };  struct abc {     int a;/*{123};*/  //compilation failed if uncommented     m; };  abc = {1, my::a}; 

compiler error, in case of uncommented text:

error: not convert ‘{1, a}’ ‘<brace-enclosed initializer list>’ ‘abc’

the below syntax:

abc = {1, my::a}; 

is list-initialization may perform differently depending on type being initialized. without non-static data member initializer (/*{123};*/), struct aggregate , case falls under [dcl.init.list]/p3:

• otherwise, if t aggregate, aggregate initialization performed.

however, aggregate type, following conditions must met in c++11:

an aggregate array or class (clause 9) no user-provided constructors (12.1), no brace-or-equal-initializers non-static data members (9.2), no private or protected non-static data members (clause 11), no base classes (clause 10), , no virtual functions (10.3).

that is, usage of nsdmi (non-static data member initialization) breaks above set of rules, , result, instance of type can no longer list-initialized.

this rule has changed in c++14, , current wording reads [dcl.init.aggr]/p1:

an aggregate array or class with

• (1.1) no user-provided, explicit, or inherited constructors ([class.ctor]),

• (1.2) no private or protected non-static data members ([class.access]),

• (1.3) no virtual functions, and

• (1.4) no virtual, private, or protected base classes ([class.mi]).

[ note: aggregate initialization not allow accessing protected , private base class' members or constructors. — end note ]

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