Can Metaprogramming Help Define Templates Based on String Conversion?

Metaprogramming: Alternative Template Selection Criteria for Function Definition

This question explores the concept of defining a template based on a type's ability to be converted to a string. The original code uses the is_arithmetic type trait, but the suggestion is to instead use a criterion that evaluates whether to_string is defined for the type.

However, the opposite of this criterion, determining when to_string is not defined, proves challenging. The following code fails:

template<typename T> enable_if_t<decltype(to_string(T{})::value, string> (T t){
    // ...
}

To address this, the answer proposes using Walter Brown's void_t type trait, which allows the creation of the following:

template<typename T, typename = void>
struct has_to_string
: std::false_type { };

template<typename T>
struct has_to_string<T, 
    void_t<decltype(std::to_string(std::declval<T>()))>
    > 
: std::true_type { };

This type trait effectively evaluates whether to_string is defined for a given type, thus providing an alternative template selection criterion that more accurately aligns with the original intent.

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