[libcxx-commits] [PATCH] D113408: [libc++] Implement P0798R8 (Monadic operations for std::optional)

[Arthur O'Dwyer via Phabricator via libcxx-commits]

Quuxplusone added inline comments.


================
Comment at: libcxx/test/std/utilities/optional/optional.monadic/or_else.pass.cpp:1
+//===----------------------------------------------------------------------===//
+//
----------------
philnik wrote:
> ldionne wrote:
> > Please add tests for SFINAE friendliness when the `Constraints:` are not met.
> Could you reference something where that is done? I have no idea what you are asking for.
Something like `libcxx/test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_value_sfinae.pass.cpp`. Basically:
```
#include "MoveOnly.h"

struct NonMovable {
    NonMovable() = default;
    NonMovable(NonMovable&&) = delete;
};

// TODO: rewrite to use 'requires' when _LIBCPP_HAS_NO_CONCEPTS goes away
template<class O, class F>
auto has_or_else(int, O&& o, F&& f)
    -> decltype(static_cast<O&&>(o).or_else(static_cast<F&&>(f)), true)
    { return true; }

template<class O, class F>
bool has_or_else(long, O&& o, F&& f)
    { return false; }

void test_sfinae() {
    std::optional<int> o1;
    std::optional<MoveOnly> o2;
    std::optional<NonMovable> o3;
    assert( has_or_else(0, o1, [&](){ return std::optional<int>(); }));
    assert( has_or_else(0, std::move(o1), [&](){ return std::optional<int>(); }));
    assert(!has_or_else(0, o2, [&](){ return std::optional<MoveOnly>(); }));
    assert( has_or_else(0, std::move(o2), [&](){ return std::optional<MoveOnly>(); }));
    assert(!has_or_else(0, o3, [&](){ return std::optional<NonMovable>(); }));
    assert(!has_or_else(0, std::move(o3), [&](){ return std::optional<NonMovable>(); }));

    assert(!has_or_else(0, o1, [&](int){ return std::optional<int>(); }));
    assert(!has_or_else(0, o1, [&](int){}));
    assert(!has_or_else(0, o1, 42));
}
```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D113408/new/

https://reviews.llvm.org/D113408