09-generics

background §

generic programming - idea that algorithm should be written once

• element abstracted
• later makes you think (parametric) polymorphism

variable, type, and function templates §

template <typename T>
struct pair {
	pair(const T& first, const T& second) : first{first}, second{second} {}
 
	T first;
	T second;
};

• template argument deduction
  • pair moreKittens = {Kitten{"Lionel", Kitten{"J"}}}
  • int smaller = min(1,2)
  • can be deduced from C++17

parameters: types, literals, templates §

• templates may be parameterized on more than types
  • literals: int, functions, references, enums

template <class T, std::size_t N>
struc

can also pass template of templates too

pragmatic usage issues §

the complete definition of a template must exist before the template is instantiated

• this is why you can’t have an implemented your functions in a seperate cpp file, they have to go in the header as well

templates are not checked until instantiated

• test templates before working important

templates have defaults -> class T = std::string, class C = std::vector<T> means that T will default for string if not given

• you want things that will be switched out on the right and not so much on the left
• this means SmallRoster<Kitten> would work for that template

methods and constructors can be templated

• need typename T::iterator * p if you want a pointer to T and not accidentaly multiply

specialization §

sometimes need type behave differently for different parameters

• generic implementations guides where necessary
• optimization (op X on matrix)
• correctness constraints
• decoupled interfaces

achieved through template specialization

namespace std {
	template < class Key >
	struct hash;
}