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Re: {}

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On 05/09/2019 00:58, Daniel wrote:
> Consider
> 
> #include <iostream>
> #include <initializer_list>
> 
> struct arg_t
> {
> };
> 
> constexpr arg_t arg = arg_t();
> 
> class C
> {
> public:
>      C(size_t n)	{}
> };
> 
> class A
> {
> public:
>      explicit A(size_t n)
>      {
> 	std::cout << "1\n";
>      }
>      A(std::initializer_list<C> item)
>      {
> 	std::cout << "2\n";
>      }
>      A(arg_t, size_t n)
>      {
>          std::cout << "3\n";
>      }
>      A(arg_t, std::initializer_list<C> item)
>      {
>          std::cout << "4\n";
>      }
> };
> 
> int main()
> {
>      A a{ { 2 } };  // (1)
>      A b{ arg, { 2 } };  // (2)
> }
> 
> Output (vs2019):
> 
> 2
> 3
> 
> I don't understand why one of these constructors is using the
> initializer_list, and the other is not. Explanation?

Does the compiler issue any warnings?

gcc gives your expected result (2,4), clang thinks you intended to call 
A(arg_t, size_t n) and issues a warning

/tmp/x.cc:40:15: warning: braces around scalar initializer 
[-Wbraced-scalar-init]
     A b{ arg, { 2 } };  // (2)
               ^~~~~~

I'm not sure which one is correct in this case!

Cheers,
Ian.

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{} Daniel <danielaparker@gmail.com> - 2019-09-04 05:58 -0700
  Re: {} Ian Collins <ian-news@hotmail.com> - 2019-09-05 06:59 +1200
    Re: {} Daniel <danielaparker@gmail.com> - 2019-09-04 12:48 -0700
    Re: {} Manfred <noname@add.invalid> - 2019-09-05 14:12 +0200
      Re: {} Öö Tiib <ootiib@hot.ee> - 2019-09-05 08:24 -0700
        Re: {} Manfred <noname@add.invalid> - 2019-09-05 20:52 +0200
        Re: {} Daniel <danielaparker@gmail.com> - 2019-09-05 13:23 -0700
          Re: {} Öö Tiib <ootiib@hot.ee> - 2019-09-05 23:44 -0700
            Re: {} Öö Tiib <ootiib@hot.ee> - 2019-09-06 02:06 -0700
              Re: {} Daniel <danielaparker@gmail.com> - 2019-09-06 11:27 -0700

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