How to allow range-for loop on my class? [duplicate]

Answer 1

The loop is defined to be equivalent to:

for ( auto __begin = ,
           __end = ;
      __begin != __end;
      ++__begin ) {
    auto& f = *__begin;
    // loop body
}

where is foo.begin(), or begin(foo) if there isn't a suitable member function, and likewise for . (This is a simplification of the specification in C++11 6.5.4, for this particular case where the range is a lvalue of class type).

So you need to define an iterator type that supports pre-increment ++it, dereference *it and comparison i1 != i2; and either

• give foo public member functions begin() and end(); or
• define non-member functions begin(foo) and end(foo), in the same namespace as foo so that they can be found by argument-dependent lookup.