[#mp_units-utility-ConstraintPolicy]
= xref:mp_units.adoc[mp_units]::xref:mp_units/utility.adoc[utility]::ConstraintPolicy
:relfileprefix: ../../
:mrdocs:

Concept satisfied by error policy types usable with xref:mp_units/utility/constrained.adoc[`constrained`].

== Synopsis

Declared in `<mp‐units/utility/constrained.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<typename EP>
concept ConstraintPolicy = requires(std::string_view msg) { EP::on_constraint_violation(msg); };
----

== Description

Requires a static `on_constraint_violation(std::string_view)` member that reports a domain constraint violation.


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