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

Sentinel default for a specializable variable‐template customization point with no usable default.

== Synopsis

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

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

== Description

A variable template cannot be `= delete`d the way a function can, so a customization point that must be specialized before use defaults to `unspecified`, and a specialization replaces it with a real value. `specified` reports whether that has happened. This is public authoring vocabulary shared by the library's own customization points and by higher‐level tools, hence it lives in the `mp_units::utility` namespace.


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