tmp/tmprso8rl7d/{from.md → to.md}
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#### Class `compare_three_way` <a id="comparisons.three.way">[[comparisons.three.way]]</a>
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In this subclause, `BUILTIN-PTR-THREE-WAY(T, U)` for types `T` and `U`
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is a boolean constant expression. `BUILTIN-PTR-THREE-WAY(T, U)` is
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`true` if and only if `<=>` in the expression
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``` cpp
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declval<T>() <=> declval<U>()
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```
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resolves to a built-in operator comparing pointers.
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``` cpp
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struct compare_three_way {
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template<class T, class U>
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requires three_way_comparable_with<T, U> || BUILTIN-PTR-THREE-WAY(T, U)
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constexpr auto operator()(T&& t, U&& u) const;
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using is_transparent = unspecified;
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};
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```
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``` cpp
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template<class T, class U>
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requires three_way_comparable_with<T, U> || BUILTIN-PTR-THREE-WAY(T, U)
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constexpr auto operator()(T&& t, U&& u) const;
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```
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*Preconditions:* If the expression
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`std::forward<T>(t) <=> std::forward<U>(u)` results in a call to a
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built-in operator `<=>` comparing pointers of type `P`, the conversion
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sequences from both `T` and `U` to `P` are
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equality-preserving [[concepts.equality]].
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*Effects:*
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- If the expression `std::forward<T>(t) <=> std::forward<U>(u)` results
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in a call to a built-in operator `<=>` comparing pointers of type `P`,
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returns `strong_ordering::less` if (the converted value of) `t`
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precedes `u` in the implementation-defined strict total order over
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pointers [[defns.order.ptr]], `strong_ordering::greater` if `u`
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precedes `t`, and otherwise `strong_ordering::equal`.
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- Otherwise, equivalent to:
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`return std::forward<T>(t) <=> std::forward<U>(u);`
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