cppdraft_translate/cppdraft/concept/assignable.md

[concept.assignable]

18 Concepts library [concepts]

18.4 Language-related concepts [concepts.lang]

18.4.8 Concept assignable_from [concept.assignable]

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template<class LHS, class RHS> concept [assignable_from](#concept:assignable_from "18.4.8 Concept assignable_­from [concept.assignable]") = is_lvalue_reference_v<LHS> && [common_reference_with](concept.commonref#concept:common_reference_with "18.4.5 Concept common_­reference_­with [concept.commonref]")<const remove_reference_t<LHS>&, const remove_reference_t<RHS>&> && requires(LHS lhs, RHS&& rhs) { { lhs = std::forward<RHS>(rhs) } -> [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<LHS>; };

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Let:

• (1.1)

lhs be an lvalue that refers to an object lcopy such that decltype((lhs)) is LHS,

• (1.2)

rhs be an expression such that decltype((rhs)) is RHS, and

• (1.3)

rcopy be a distinct object that is equal to rhs.

LHS and RHS modelassignable_from<LHS, RHS> only if

• (1.4)

  addressof(lhs = rhs) == addressof(lcopy).

• (1.5)

  After evaluating lhs = rhs:

  • (1.5.1)

    lhs is equal to rcopy, unless rhs is a non-const xvalue that refers to lcopy.

  • (1.5.2)

    If rhs is a non-const xvalue, the resulting state of the object to which it refers is valid but unspecified ([lib.types.movedfrom]).

  • (1.5.3)

    Otherwise, if rhs is a glvalue, the object to which it refers is not modified.

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[Note 1:

Assignment need not be a total function ([structure.requirements]); in particular, if assignment to an object x can result in a modification of some other object y, then x = y is likely not in the domain of =.

— end note]