[#bsl-operator_3way-070]
= xref:bsl.adoc[bsl]::operator<=>
:relfileprefix: ../
:mrdocs:

Perform a three‐way comparison of the specified `lhs` and the specified `rhs` objects by using the comparison operators of `t_LHS` and `t_RHS`; return the result of that comparison. This function can be called in constant expressions only if `t_LHS` is not allocator‐aware.

== Synopsis

Declared in `<bslstl_optional.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_LHS,
    class t_RHS>
requires (!BloombergLP::bslstl::Optional_DerivedFromOptional<t_RHS>) &&
         three_way_comparable_with<t_LHS, t_RHS>
constexpr
compare_three_way_result_t<t_LHS, t_RHS>
operator<=>(
    xref:bsl/optional-072.adoc[bsl::optional<t_LHS>] const& lhs,
    t_RHS const& rhs);
----


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