73ef4ff3
 Hu Chunming
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# stl_interfaces
An updated C++20-friendly version of the `iterator_facade` and
`iterator_adaptor` parts of Boost.Iterator (now called `iterator_interface`);
a pre-C++20 version of C++20's `view_interface`; and a new template called
`container_interface`, meant to aid the creation of new containers; all
targeting standardization. This library requires at least C++14.
For the iterator portion -- if you need to write an iterator, `iterator_interface` turns this:
```c++
struct repeated_chars_iterator
{
using value_type = char;
using difference_type = std::ptrdiff_t;
using pointer = char const *;
using reference = char const;
using iterator_category = std::random_access_iterator_tag;
constexpr repeated_chars_iterator() noexcept :
first_(nullptr),
size_(0),
n_(0)
{}
constexpr repeated_chars_iterator(
char const * first,
difference_type size,
difference_type n) noexcept :
first_(first),
size_(size),
n_(n)
{}
constexpr reference operator*() const noexcept
{
return first_[n_ % size_];
}
constexpr value_type operator[](difference_type n) const noexcept
{
return first_[(n_ + n) % size_];
}
constexpr repeated_chars_iterator & operator++() noexcept
{
++n_;
return *this;
}
constexpr repeated_chars_iterator operator++(int)noexcept
{
repeated_chars_iterator retval = *this;
++*this;
return retval;
}
constexpr repeated_chars_iterator & operator+=(difference_type n) noexcept
{
n_ += n;
return *this;
}
constexpr repeated_chars_iterator & operator--() noexcept
{
--n_;
return *this;
}
constexpr repeated_chars_iterator operator--(int)noexcept
{
repeated_chars_iterator retval = *this;
--*this;
return retval;
}
constexpr repeated_chars_iterator & operator-=(difference_type n) noexcept
{
n_ -= n;
return *this;
}
friend constexpr bool operator==(
repeated_chars_iterator lhs, repeated_chars_iterator rhs) noexcept
{
return lhs.first_ == rhs.first_ && lhs.n_ == rhs.n_;
}
friend constexpr bool operator!=(
repeated_chars_iterator lhs, repeated_chars_iterator rhs) noexcept
{
return !(lhs == rhs);
}
friend constexpr bool operator<(
repeated_chars_iterator lhs, repeated_chars_iterator rhs) noexcept
{
return lhs.first_ == rhs.first_ && lhs.n_ < rhs.n_;
}
friend constexpr bool operator<=(
repeated_chars_iterator lhs, repeated_chars_iterator rhs) noexcept
{
return lhs == rhs || lhs < rhs;
}
friend constexpr bool operator>(
repeated_chars_iterator lhs, repeated_chars_iterator rhs) noexcept
{
return rhs < lhs;
}
friend constexpr bool operator>=(
repeated_chars_iterator lhs, repeated_chars_iterator rhs) noexcept
{
return rhs <= lhs;
}
friend constexpr repeated_chars_iterator
operator+(repeated_chars_iterator lhs, difference_type rhs) noexcept
{
return lhs += rhs;
}
friend constexpr repeated_chars_iterator
operator+(difference_type lhs, repeated_chars_iterator rhs) noexcept
{
return rhs += lhs;
}
friend constexpr repeated_chars_iterator
operator-(repeated_chars_iterator lhs, difference_type rhs) noexcept
{
return lhs -= rhs;
}
friend constexpr difference_type operator-(
repeated_chars_iterator lhs, repeated_chars_iterator rhs) noexcept
{
return lhs.n_ - rhs.n_;
}
private:
char const * first_;
difference_type size_;
difference_type n_;
};
```
into this:
```c++
struct repeated_chars_iterator : boost::stl_interfaces::iterator_interface<
repeated_chars_iterator,
std::random_access_iterator_tag,
char,
char>
{
constexpr repeated_chars_iterator() noexcept :
first_(nullptr),
size_(0),
n_(0)
{}
constexpr repeated_chars_iterator(
char const * first, difference_type size, difference_type n) noexcept :
first_(first),
size_(size),
n_(n)
{}
constexpr char operator*() const noexcept { return first_[n_ % size_]; }
constexpr repeated_chars_iterator & operator+=(std::ptrdiff_t i) noexcept
{
n_ += i;
return *this;
}
constexpr auto operator-(repeated_chars_iterator other) const noexcept
{
return n_ - other.n_;
}
private:
char const * first_;
difference_type size_;
difference_type n_;
};
```
The code size savings are even more dramatic for `view_interface` and
`container_interface`! If you don't ever write iterators, views, containers,
or view adaptors, this is not for you.
This library includes both C++20 concept constrained and SFINAE-constrained
versions.
[](LICENSE_1_0.txt)
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