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

Policy that checks the value is ≥ 0 and reports violations.

== Synopsis

Declared in `<mp‐units/overflow_policies.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
struct check_non_negative;
----

== Description

Intended for quantities that are inherently non‐negative (e.g., _length_, _mass_, _duration_). Automatically applied to `natural_point_origin<QS>` when `QS` is tagged `non_negative` in the ISQ.

If the quantity's representation type has a `constraint_violation_handler` specialization, the handler's `on_violation()` is called on negative values (providing guaranteed enforcement regardless of build mode). Otherwise, falls back to `MP_UNITS_PRECONDITION`, which may be disabled in release builds.

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:mp_units/check_non_negative/operator_call.adoc[`operator()`] 
| Checks that `v` is non‐negative and reports a violation otherwise.
|===


== Data Members

[cols="1,4"]
|===
| Name| Description
| xref:mp_units/check_non_negative/min.adoc[`min`] 
| Lower domain bound: zero in any unit. Consumed by quantity_point::min() and std::numeric_limits<quantity_point>::lowest(). The operator() uses V::zero() directly (no unit scaling needed); this member exists solely for the numeric_limits interface.
|===



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