1. when it needs to be done at compile-time
Metaprogramming
when it needs to be done at compile-time

2. Metaprogramming programming to be executed at compile-time
in C++ done with templates, hence template metaprogramming (TMP)
optimizes code at compile-time, possibly faster
compilation is slower
some programming work is delegated to compiler
resultant code is easier(?) to understand

3. Preliminaries
decltype(expression) – returns type of expression, C++11 addition
recursive template – a template may be invoked inside the template
stopping case provided as specialization
non-type parameter for template instantiation – used for template recursion
treated as a constant
std::function is defined in <functional> is used to create function types, to be used as template parameters
syntax
std::function<returnValueType (argTypes…)>
example
std::function <void(int, const string&)> f1 = func;

4. Template Specialization
may need to implement specific actions for particular type
specialization – overrides generic classes or method
may specialize either whole template
template<>
class Stack<char, 100> { … };
or individual methods
void Stack<char>::input(){…}
why not use non-templated classes for specific types?
specialization provides uniform interface to template users
may only need specialization on individual methods

5. Examples
branching
factorial
loop unrolling