Can't use enum class as unordered_map key

Question

I have a class containing an enum class.

class Shader {
public:
    enum class Type {
        Vertex   = GL_VERTEX_SHADER,
        Geometry = GL_GEOMETRY_SHA         


        

Answer 1

As KerrekSB pointed out, you need to provide a specialization of std::hash if you want to use std::unordered_map, something like:

namespace std
{
    template<>
    struct hash< ::Shader::Type >
    {
        typedef ::Shader::Type argument_type;
        typedef std::underlying_type< argument_type >::type underlying_type;
        typedef std::hash< underlying_type >::result_type result_type;
        result_type operator()( const argument_type& arg ) const
        {
            std::hash< underlying_type > hasher;
            return hasher( static_cast< underlying_type >( arg ) );
        }
    };
}