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_SHADER,
        Fragment = GL_FRAGMENT_SHADER
    };
    //...

Then, when I implement the following code in another class...

std::unordered_map<Shader::Type, Shader> shaders;

...I get a compile error.

...usr/lib/c++/v1/type_traits:770:38: 
Implicit instantiation of undefined template 'std::__1::hash<Shader::Type>'

What is causing the error here?

Answer 1

Try

std::unordered_map<Shader::Type, Shader, std::hash<std::underlying_type<Shader::Type>::type>> shaders;