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gsl::at clean-up: (#479)

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* initializer_list overload returns by value to avoid lifetime issues

* generic overload uses expression SFINAE to work with any type that has member size() and operator[], which notably includes const/non-const vector and array.

* Add test coverage for const objects, rvalue initializer_lists, and constexpr usage.

Fixes #357.
This commit is contained in:
Casey Carter
2017-04-03 22:43:43 -07:00
committed by Neil MacIntosh
parent d65660760b
commit ebab8cab7f
2 changed files with 81 additions and 48 deletions
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include/gsl/gsl_util
+6 -12
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@@ -127,31 +127,25 @@ inline T narrow(U u)
}
//
// at() - Bounds-checked way of accessing static arrays, std::array, std::vector
// at() - Bounds-checked way of accessing builtin arrays, std::array, std::vector
//
template <class T, std::size_t N>
inline constexpr T& at(T (&arr)[N], std::ptrdiff_t index)
{
Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(N));
return arr[static_cast<std::size_t>(index)];
}
template <class T, std::size_t N>
inline constexpr T& at(std::array<T, N>& arr, std::ptrdiff_t index)
inline constexpr T& at(T (&arr)[N], const std::ptrdiff_t index)
{
Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(N));
return arr[static_cast<std::size_t>(index)];
}
template <class Cont>
inline constexpr typename Cont::value_type& at(Cont& cont, std::ptrdiff_t index)
inline constexpr auto at(Cont& cont, const std::ptrdiff_t index) -> decltype(cont[cont.size()])
{
Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(cont.size()));
return cont[static_cast<typename Cont::size_type>(index)];
using size_type = decltype(cont.size());
return cont[static_cast<size_type>(index)];
}
template <class T>
inline constexpr const T& at(std::initializer_list<T> cont, std::ptrdiff_t index)
inline constexpr T at(const std::initializer_list<T> cont, const std::ptrdiff_t index)
{
Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(cont.size()));
return *(cont.begin() + index);