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[wpiutil] SpanExtras: Add take_back and take_front (#5651)

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Also allow sized spans as input (return is always dynamic size).
This commit is contained in:
Peter Johnson
2023-09-17 20:00:31 -07:00
committed by GitHub
parent 17f1062885
commit 3b51ecc35b
1 changed files with 34 additions and 4 deletions
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38
wpiutil/src/main/native/include/wpi/SpanExtras.h
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@@ -10,19 +10,49 @@
namespace wpi {
/// Drop the first \p N elements of the array.
template <typename T>
constexpr std::span<T> drop_front(std::span<T> in,
template <typename T, size_t N>
constexpr std::span<T> drop_front(std::span<T, N> in,
typename std::span<T>::size_type n = 1) {
assert(in.size() >= n && "Dropping more elements than exist");
return in.subspan(n, in.size() - n);
}
/// Drop the last \p N elements of the array.
template <typename T>
constexpr std::span<T> drop_back(std::span<T> in,
template <typename T, size_t N>
constexpr std::span<T> drop_back(std::span<T, N> in,
typename std::span<T>::size_type n = 1) {
assert(in.size() >= n && "Dropping more elements than exist");
return in.subspan(0, in.size() - n);
}
/**
* Returns a span equal to @p in but with only the first @p n
* elements remaining. If @p n is greater than the length of the
* span, the entire span is returned.
*/
template <typename T, size_t N>
constexpr std::span<T> take_front(std::span<T, N> in,
typename std::span<T>::size_type n = 1) {
auto length = in.size();
if (n >= length) {
return in;
}
return drop_back(in, length - n);
}
/**
* Returns a span equal to @p in but with only the last @p n
* elements remaining. If @p n is greater than the length of the
* span, the entire span is returned.
*/
template <typename T, size_t N>
constexpr std::span<T> take_back(std::span<T, N> in,
typename std::span<T>::size_type n = 1) {
auto length = in.size();
if (n >= length) {
return in;
}
return drop_front(in, length - n);
}
} // namespace wpi