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

Sentinel type indicating no default implementation for a variable template

== Synopsis

Declared in `<mp‐units/framework/customization_points.h>`

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

This type is used as a placeholder for primary variable templates that should not have a default implementation, working around the language limitation that variable templates cannot be "deleted" like functions can.


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