Skip to content

Add remove_prefix and remove_suffix (P3729) #8

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
ssam18 merged 3 commits into from
May 1, 2026
Merged

Add remove_prefix and remove_suffix (P3729) #8

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
fb53441
Add remove_prefix and remove_suffix (P3729)
ssam18 Apr 26, 2026
6928940
Merge branch 'main' into remove-prefix-suffix-p3729
ssam18 May 1, 2026
cd59340
Use C++20 requires clauses for remove_prefix/remove_suffix
ssam18 May 1, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
15 changes: 15 additions & 0 deletions include/beman/span/span.hpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -210,6 +210,21 @@ class span {
return {data_ + offset, count == dynamic_extent ? size() - offset : count};
}

constexpr void remove_prefix(size_type n) noexcept
requires(Extent == dynamic_extent)
{
assert(n <= size());
data_ += n;
size_ -= n;
}

constexpr void remove_suffix(size_type n) noexcept
requires(Extent == dynamic_extent)
{
assert(n <= size());
size_ -= n;
}

// 26.7.3.4 Observers [span.obs]

[[nodiscard]] constexpr size_type size() const noexcept { return size_; }
Expand Down
103 changes: 97 additions & 6 deletions tests/beman/span/span.test.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,8 @@
#include <array>
#include <cstddef>
#include <numeric>
#include <type_traits>
#include <utility>
#include <vector>

namespace bsp = beman::span;
Expand Down Expand Up @@ -203,29 +205,29 @@ TEST(SpanElementAccess, write_through_span) {

// at() bounds-checked access (P2821R5, C++26)
TEST(SpanAt, in_bounds_returns_element) {
int arr[] = {10, 20, 30};
int arr[] = {10, 20, 30};
bsp::span<int> s(arr);
EXPECT_EQ(s.at(0), 10);
EXPECT_EQ(s.at(1), 20);
EXPECT_EQ(s.at(2), 30);
}

TEST(SpanAt, returns_lvalue_reference_for_mutable_span) {
int arr[] = {1, 2, 3};
int arr[] = {1, 2, 3};
bsp::span<int> s(arr);
s.at(1) = 42;
EXPECT_EQ(arr[1], 42);
static_assert(std::is_same_v<decltype(s.at(0)), int&>);
}

TEST(SpanAt, throws_out_of_range_at_size_boundary) {
int arr[] = {1, 2, 3};
int arr[] = {1, 2, 3};
bsp::span<int> s(arr);
EXPECT_THROW(s.at(3), std::out_of_range);
}

TEST(SpanAt, throws_out_of_range_well_past_size) {
int arr[] = {1, 2, 3};
int arr[] = {1, 2, 3};
bsp::span<int> s(arr);
EXPECT_THROW(s.at(100), std::out_of_range);
}
Expand All @@ -236,14 +238,14 @@ TEST(SpanAt, empty_span_always_throws) {
}

TEST(SpanAt, fixed_extent_in_bounds_and_out_of_range) {
int arr[] = {7, 8, 9, 10};
int arr[] = {7, 8, 9, 10};
bsp::span<int, 4> s(arr);
EXPECT_EQ(s.at(3), 10);
EXPECT_THROW(s.at(4), std::out_of_range);
}

TEST(SpanAt, const_span_returns_reference_to_const) {
const int arr[] = {1, 2, 3};
const int arr[] = {1, 2, 3};
bsp::span<const int> s(arr);
EXPECT_EQ(s.at(2), 3);
static_assert(std::is_same_v<decltype(s.at(0)), const int&>);
Expand Down Expand Up @@ -413,6 +415,95 @@ TEST(SpanSubviews, subspan_dynamic_to_end) {
EXPECT_EQ(sub[1], 4);
}

// ---------------------------------------------------------------------------
// remove_prefix / remove_suffix (P3729)
// ---------------------------------------------------------------------------

TEST(SpanModifiers, remove_prefix_zero_is_noop) {
int arr[] = {1, 2, 3, 4, 5};
bsp::span<int> s(arr);
s.remove_prefix(0);
EXPECT_EQ(s.size(), 5u);
EXPECT_EQ(s.data(), arr);
}

TEST(SpanModifiers, remove_prefix_partial) {
int arr[] = {1, 2, 3, 4, 5};
bsp::span<int> s(arr);
s.remove_prefix(2);
EXPECT_EQ(s.size(), 3u);
EXPECT_EQ(s.data(), arr + 2);
EXPECT_EQ(s[0], 3);
EXPECT_EQ(s[2], 5);
}

TEST(SpanModifiers, remove_prefix_full_empties_span) {
int arr[] = {1, 2, 3};
bsp::span<int> s(arr);
s.remove_prefix(s.size());
EXPECT_EQ(s.size(), 0u);
EXPECT_TRUE(s.empty());
}

TEST(SpanModifiers, remove_suffix_zero_is_noop) {
int arr[] = {1, 2, 3, 4, 5};
bsp::span<int> s(arr);
s.remove_suffix(0);
EXPECT_EQ(s.size(), 5u);
EXPECT_EQ(s.data(), arr);
}

TEST(SpanModifiers, remove_suffix_partial) {
int arr[] = {1, 2, 3, 4, 5};
bsp::span<int> s(arr);
s.remove_suffix(2);
EXPECT_EQ(s.size(), 3u);
EXPECT_EQ(s.data(), arr);
EXPECT_EQ(s[0], 1);
EXPECT_EQ(s[2], 3);
}

TEST(SpanModifiers, remove_suffix_full_empties_span) {
int arr[] = {1, 2, 3};
bsp::span<int> s(arr);
s.remove_suffix(s.size());
EXPECT_EQ(s.size(), 0u);
EXPECT_TRUE(s.empty());
}

TEST(SpanModifiers, remove_prefix_and_suffix_combined) {
int arr[] = {10, 20, 30, 40, 50, 60};
bsp::span<int> s(arr);
s.remove_prefix(1);
s.remove_suffix(2);
EXPECT_EQ(s.size(), 3u);
EXPECT_EQ(s[0], 20);
EXPECT_EQ(s[2], 40);
}

namespace modifiers_detail {
template <class T, class = void>
struct has_remove_prefix : std::false_type {};

template <class T>
struct has_remove_prefix<T, std::void_t<decltype(std::declval<T&>().remove_prefix(std::size_t{0}))>> : std::true_type {
};

template <class T, class = void>
struct has_remove_suffix : std::false_type {};

template <class T>
struct has_remove_suffix<T, std::void_t<decltype(std::declval<T&>().remove_suffix(std::size_t{0}))>> : std::true_type {
};
} // namespace modifiers_detail

TEST(SpanModifiers, fixed_extent_has_no_modifiers) {
static_assert(modifiers_detail::has_remove_prefix<bsp::span<int>>::value);
static_assert(modifiers_detail::has_remove_suffix<bsp::span<int>>::value);
static_assert(!modifiers_detail::has_remove_prefix<bsp::span<int, 3>>::value);
static_assert(!modifiers_detail::has_remove_suffix<bsp::span<int, 3>>::value);
}

// ---------------------------------------------------------------------------
// as_bytes / as_writable_bytes
// ---------------------------------------------------------------------------
Expand Down