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45 lines
1.3 KiB
45 lines
1.3 KiB
#pragma once
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// Many C++20 std headers define ssize; pick one. This is needed even to
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// get the __cpp_lib_ssize define set.
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#include <vector>
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#ifdef __cpp_lib_ssize
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namespace drake {
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using std::ssize;
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} // namespace drake
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#else // __cpp_lib_ssize
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#include <cstddef> // For std::ptrdiff_t
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#include <type_traits> // For std::common_type_t, std::make_signed_t
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namespace drake {
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/** Implements C++20 %std::ssize() for earlier compilers. See
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https://en.cppreference.com/w/cpp/iterator/size for documentation. Will be
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removed once all Drake-supported platforms offer %std::ssize(). */
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// The implementations below are taken directly from the cppreference
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// documentation. BTW std::size() is already supported on all Drake platforms.
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template <class C>
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constexpr auto ssize(const C& c)
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-> std::common_type_t<std::ptrdiff_t,
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std::make_signed_t<decltype(c.size())> > {
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using R = std::common_type_t<std::ptrdiff_t,
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std::make_signed_t<decltype(c.size())> >;
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return static_cast<R>(c.size());
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}
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/** This signature returns the size of built-in (C style) arrays. */
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template <class T, std::ptrdiff_t N>
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constexpr std::ptrdiff_t ssize(const T (&array)[N]) noexcept {
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return N;
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}
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} // namespace drake
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#endif // __cpp_lib_ssize
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