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#include <utility>
#include <concepts>
//comparable
template <typename Type>
concept Comparable =
requires (Type lhs, Type rhs)
{
lhs == rhs;
lhs != rhs;
};
template <typename Type>
concept Incrementable =
requires (Type type)
{
++type;
type++;
};
//=
//dereference
template <typename Type>
concept Dereferenceable =
requires(Type type)
{
{ *type } -> std::same_as<typename Type::value_type &>;
};
//=
//constderef
template <typename Type>
concept ConstDereferenceable =
requires(Type const &type)
{
{ *type } -> std::same_as<typename Type::value_type const &>;
};
//=
struct InIt
{
typedef int value_type;
InIt &operator++();
InIt operator++(int);
int const &operator*() const;
};
bool operator==(InIt const &lh, InIt const &rh);
bool operator!=(InIt const &lh, InIt const &rh);
int operator-(InIt const &lh, InIt const &rh);
//initerator
template <typename Type>
concept InIterator =
Comparable<Type> and Incrementable<Type> and
ConstDereferenceable<Type>;
template <InIterator Type>
void inFun(Type tp)
{}
//=
struct OutIt: public InIt
{
int &operator*();
};
//outiterator
template <typename Type>
concept OutIterator =
Comparable<Type> and Incrementable<Type> and
Dereferenceable<Type>;
template <OutIterator Type>
void outFun(Type tp)
{}
//=
//fwditerator
template <typename Type>
concept FwdIterator =
InIterator<Type> and OutIterator<Type>;
struct FwdIt: public OutIt
{
using OutIt::operator*;
using InIt::operator*;
};
template <FwdIterator Type>
void fwdFun(Type tp)
{}
//=
//iterable
struct Iterable
{
typedef int value_type;
Iterable &operator++();
Iterable operator++(int);
int const &operator*() const;
int &operator*();
};
bool operator==(Iterable const &lh, Iterable const &rh);
bool operator!=(Iterable const &lh, Iterable const &rh);
int operator-(Iterable const &lh, Iterable const &rh);
//=
//bidir
template <typename Type>
concept BiIterator =
FwdIterator<Type> and
requires(Type type)
{
--type;
type--;
};
template <typename Type>
concept RndIterator =
BiIterator<Type>
and
requires(Type lhs, Type rhs)
{
lhs += 0;
lhs -= 0;
lhs + 0;
lhs - 0;
{ lhs - rhs } -> std::same_as<int>;
};
//=
struct BiIt: public FwdIt
{
InIt &operator--();
InIt operator--(int);
};
template <BiIterator Type>
void biFun(Type tp)
{}
//randomit
struct RndIt: public BiIt
{
RndIt &operator+=(int);
RndIt &operator-=(int);
};
RndIt &operator+(RndIt const &lh, int);
RndIt &operator-(RndIt const &lh, int);
template <RndIterator Type>
void rndFun(Type tp)
{}
int main()
{
inFun(InIt{});
// outFun(InIt{}); // WC: unsatisfied constraint
outFun(OutIt{});
// fwdFun(OutIt{}); // WC
fwdFun(FwdIt{});
inFun(Iterable{});
outFun(Iterable{});
fwdFun(Iterable{});
biFun(BiIt{});
// biFun(InIt{}); // WC
// biFun(OutIt{}); // WC
rndFun(RndIt{});
biFun(RndIt{}); // OK: extra functions are fine
}
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