[#mp_units-undefined_t]
= xref:mp_units.adoc[mp&lowbar;units]::undefined&lowbar;t
:relfileprefix: ../
:mrdocs:

Sentinel type indicating no default implementation for a variable template

== Synopsis

Declared in `&lt;mp&hyphen;units&sol;framework&sol;customization&lowbar;points&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
struct undefined&lowbar;t;
----

== 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 &quot;deleted&quot; like functions can&period;


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