Type Traits: Compile-Time Type Analysis

Creating a Custom Type Trait to Check for a Member Function

How can I create a custom type trait to check if a type has a specific member function?

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To create a custom type trait that checks for the presence of a specific member function in a type, you can use SFINAE (Substitution Failure Is Not An Error) techniques. Here's an example of how to create a type trait has_render that checks if a type has a Render member function:

#include <iostream>
#include <type_traits>

// Helper struct for SFINAE
template <typename T>
struct has_render {
  template <typename U>
  static auto test(U* p)
    -> decltype(p->Render(), std::true_type{});

  template <typename>
  static std::false_type test(...);

  static constexpr bool value =

// _v version for convenience
template <typename T>
inline constexpr bool has_render_v =

// Example classes
class WithRender {
  void Render() {}

class WithoutRender {};

int main() {
  std::cout << std::boolalpha;
  std::cout << "WithRender has Render: "
    << has_render_v<WithRender> << "\n";
  std::cout << "WithoutRender has Render: "
    << has_render_v<WithoutRender> << "\n";
WithRender has Render: true
WithoutRender has Render: false

In this example, the has_render struct uses SFINAE to detect the presence of a Render member function. The test function is overloaded based on whether Render can be called on a pointer to the type T. If Render is present, the first overload is selected, and std::true_type is returned. Otherwise, the second overload is selected, and std::false_type is returned.

The has_render_v variable template is provided for convenience, similar to the _v suffix used in standard library type traits.

This technique can be adapted to check for the presence of other member functions or member variables in a type.

Answers to questions are automatically generated and may not have been reviewed.

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