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Add [[nodiscard]] to tl::expected (#165)

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* test: Silence "non-void function does not return a value"

* Add [[nodiscard]] to tl::expected

Microsoft STL added [[nodiscard]] on 2024-12-13;
see https://github.com/microsoft/STL/pull/5174

martinmoene/expected-lite added [[nodiscard]] on 2024-12-10;
see https://github.com/martinmoene/expected-lite/pull/74
This commit is contained in:
Arthur O'Dwyer
2025-07-12 05:22:33 -04:00
committed by GitHub
parent 17d0058a5a
commit 2aa40964ba
3 changed files with 13 additions and 12 deletions
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5
include/tl/expected.hpp
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@@ -133,7 +133,7 @@ struct is_trivially_copy_constructible<std::vector<T, A>> : std::false_type {};
#endif #endif
namespace tl { namespace tl {
template <class T, class E> class expected; template <class T, class E> class [[nodiscard]] expected;
#ifndef TL_MONOSTATE_INPLACE_MUTEX #ifndef TL_MONOSTATE_INPLACE_MUTEX
#define TL_MONOSTATE_INPLACE_MUTEX #define TL_MONOSTATE_INPLACE_MUTEX
@@ -1276,7 +1276,8 @@ private:
/// has been destroyed. The initialization state of the contained object is /// has been destroyed. The initialization state of the contained object is
/// tracked by the expected object. /// tracked by the expected object.
template <class T, class E> template <class T, class E>
class expected : private detail::expected_move_assign_base<T, E>, class [[nodiscard]] expected :
private detail::expected_move_assign_base<T, E>,
private detail::expected_delete_ctor_base<T, E>, private detail::expected_delete_ctor_base<T, E>,
private detail::expected_delete_assign_base<T, E>, private detail::expected_delete_assign_base<T, E>,
private detail::expected_default_ctor_base<T, E> { private detail::expected_default_ctor_base<T, E> {

4
tests/extensions.cpp
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@@ -814,7 +814,7 @@ struct F {
TEST_CASE("14", "[issue.14]") { TEST_CASE("14", "[issue.14]") {
auto res = tl::expected<S,F>{tl::unexpect, F{}}; auto res = tl::expected<S,F>{tl::unexpect, F{}};
res.map_error([](F f) { (void)res.map_error([](F f) {
(void)f; (void)f;
}); });
} }
@@ -822,7 +822,7 @@ TEST_CASE("14", "[issue.14]") {
TEST_CASE("32", "[issue.32]") { TEST_CASE("32", "[issue.32]") {
int i = 0; int i = 0;
tl::expected<void, int> a; tl::expected<void, int> a;
a.map([&i]{i = 42;}); (void)a.map([&i]{i = 42;});
REQUIRE(i == 42); REQUIRE(i == 42);
auto x = a.map([]{return 42;}); auto x = a.map([]{return 42;});

14
tests/issues.cpp
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@@ -13,7 +13,7 @@ tl::expected<int, string> getInt2(int val) { return val; }
tl::expected<int, string> getInt1() { return getInt2(5).and_then(getInt3); } tl::expected<int, string> getInt1() { return getInt2(5).and_then(getInt3); }
TEST_CASE("Issue 1", "[issues.1]") { getInt1(); } TEST_CASE("Issue 1", "[issues.1]") { (void)getInt1(); }
tl::expected<int, int> operation1() { return 42; } tl::expected<int, int> operation1() { return 42; }
@@ -22,7 +22,7 @@ tl::expected<std::string, int> operation2(int const val) { (void)val; return "Ba
TEST_CASE("Issue 17", "[issues.17]") { TEST_CASE("Issue 17", "[issues.17]") {
auto const intermediate_result = operation1(); auto const intermediate_result = operation1();
intermediate_result.and_then(operation2); (void)intermediate_result.and_then(operation2);
} }
struct a {}; struct a {};
@@ -61,7 +61,7 @@ tl::expected<int, std::string> error() {
std::string maperror(std::string s) { return s + "maperror "; } std::string maperror(std::string s) { return s + "maperror "; }
TEST_CASE("Issue 30", "[issues.30]") { TEST_CASE("Issue 30", "[issues.30]") {
error().map_error(maperror); (void)error().map_error(maperror);
} }
struct i31{ struct i31{
@@ -91,7 +91,7 @@ void errorhandling(std::string){}
TEST_CASE("Issue 34", "[issues.34]") { TEST_CASE("Issue 34", "[issues.34]") {
tl::expected <int, std::string> result = voidWork () tl::expected <int, std::string> result = voidWork ()
.and_then (work2); .and_then (work2);
result.map_error ([&] (std::string result) {errorhandling (result);}); (void)result.map_error ([&] (std::string result) {errorhandling (result);});
} }
struct non_copyable { struct non_copyable {
@@ -101,7 +101,7 @@ struct non_copyable {
}; };
TEST_CASE("Issue 42", "[issues.42]") { TEST_CASE("Issue 42", "[issues.42]") {
tl::expected<non_copyable,int>{}.map([](non_copyable) {}); (void)tl::expected<non_copyable,int>{}.map([](non_copyable) {});
} }
TEST_CASE("Issue 43", "[issues.43]") { TEST_CASE("Issue 43", "[issues.43]") {
@@ -144,12 +144,12 @@ struct move_tracker {
move_tracker() = default; move_tracker() = default;
move_tracker(move_tracker const &other) noexcept {}; move_tracker(move_tracker const &other) noexcept;
move_tracker(move_tracker &&orig) noexcept move_tracker(move_tracker &&orig) noexcept
: moved(orig.moved + 1) {} : moved(orig.moved + 1) {}
move_tracker & move_tracker &
operator=(move_tracker const &other) noexcept {}; operator=(move_tracker const &other) noexcept;
move_tracker &operator=(move_tracker &&orig) noexcept { move_tracker &operator=(move_tracker &&orig) noexcept {
moved = orig.moved + 1; moved = orig.moved + 1;