Template Parameter: Variadic Templates

A variadic template is a template with an arbitrary number of parameters.

template <typename ... Args>
void variadicTemplate(Args ... args){ . . . . }

Parameter pack

• By using the ellipse (…) Args- or args becomes a parameter pack
• Args is a template parameter pack, and args is a function parameter pack
• Parameter packs can only be packed or unpacked
• If the ellipse is left from Args, the parameter pack will be packed. If the ellipse is right from Arge, the parameter pack will be unpacked.

The compiler can automatically deduce the template arguments.

Variadic Templates are often used in the Standard Template Library:

• sizeof-Operator, std::tuple, std::thread

The usage of parameter packs obeys a typical pattern.

• Perform an operation on the first element of the parameter pack and recursively invoke the operation on the remaining elements.
• The recursion ends after a finite number of steps.
• The boundary condition is typically a fully specialized template.