c++ - Empty struct or anonymous struct as tag -

is there difference in use between defining tag type anonymous empty struct or empty struct?

using = struct {}; struct b {}; 

at mind difference "effective" type name, when 1 utilize kind of reflection (i.e. __pretty_function__, <cxxabi.h>:abi::__cxa_demangle(typeid().name()) etc).

adl work both ways:

namespace ns {  using = struct {}; struct b {};  constexpr bool adl(a) {     return true; }  constexpr bool adl(b) {     return true; }  }  template< typename type > constexpr bool adl(type) {     return false; }  static_assert(adl(ns::a{})); static_assert(adl(ns::b{})); 

apart different strings you've noted, significant difference can refer b using elaborated-type-specifier, can struct b b; instead of b b; cannot use struct a; because a typedef-name not class-name.

however there never reason struct b instead of b in practice difference not important, not tag types.