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Remove double forward #1387

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Merged
merged 2 commits into from
Jan 22, 2024
Merged

Remove double forward #1387

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02779d6
Remove double forward
sylveon Jan 17, 2024
27f0f71
Fix compilation issues
sylveon Jan 17, 2024
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10 changes: 8 additions & 2 deletions strings/base_string.h
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Original file line number Diff line number Diff line change
Expand Up @@ -567,12 +567,18 @@ namespace winrt::impl
template <typename... Args>
inline hstring base_format(Args&&... args)
{
auto const size = std::formatted_size(std::forward<Args>(args)...);
// don't forward because an object could be moved-from, causing issues
// for the second format call.
// not forwarding lets us take both rvalues and lvalues but pass them
// further down as an lvalue ref. some types can only be formatted
// when non-const (e.g. ranges::filter_view) so take a const reference
// as parameter wouldn't work for all scenarios.
auto const size = std::formatted_size(args...);
WINRT_ASSERT(size < UINT_MAX);
auto const size32 = static_cast<uint32_t>(size);

hstring_builder builder(size32);
WINRT_VERIFY_(size32, std::format_to_n(builder.data(), size32, std::forward<Args>(args)...).size);
WINRT_VERIFY_(size32, std::format_to_n(builder.data(), size32, args...).size);
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It seems like you could still forward here. Although I guess without the first forward there's not much point anymore...?

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While formatters don't care about value category, apparently std::format_string does. So forwarding in one place but not the other would break it (like it currently is).

return builder.to_hstring();
}
#endif
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