pimpl for a templated class

Question

I want to use the pimpl idiom to avoid having users of my library need our external dependencies (like boost, etc) however when my class is templated that seems to be imposs

Answer 1

You can explicitly instantiate templates in the source file, but that is possible only if you know what the template type is going to be. Otherwise, do not use pimpl idiom for templates.

Something like this :

header.hpp :

#ifndef HEADER_HPP
#define HEADER_HPP

template< typename T >
class A
{
  // constructor+methods + pimpl
};

#endif

source.cpp :

#include "header.hpp"

// implementation

// explicitly instantiate for types that will be used
template class A< int >;
template class A< float >;
// etc...