Templates in C++

Generic programming is programming using types and algorithms parameterized by types, values, and algorithms. Templates Core Guidelines

Note: Use Templates if you have a realistic need for more than one template argument type.

In this “prototype” example, the keywords template to specify a generic function and typename (could also be class) a generic type, which get expanded at compile time to code with types that are passed as parameters.

template<typename T>
T Min(T a, T b)
{
  return (a < b) ? a : b;
}

assert(Min<double>(3.5,5.0) == 3.5);
assert(Min<int>(4,2) == 2);

Deduction

Without explicitly identifying the types, deduction occurs:

assert(Min(3.5,5.0) == 3.5);
assert(Min(4,2) == 2);

Template Class

A templatized class uses a “templatized” constructor, for example vector is a generic class.

Concepts

Templates can express anything (at compile time), but had “lousy” interfaces. To precisely express requirements of templates C++20 introduces concepts.