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

Checks whether a quantity of quantity spec `From` can be cast to quantity spec `To`

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    xref:mp_units/QuantitySpec.adoc[QuantitySpec] From,
    xref:mp_units/QuantitySpec.adoc[QuantitySpec] To>
[[nodiscard]]
consteval
bool
castable(
    From from,
    To to);
----

== Description

`castable` is a weaker requirement than xref:mp_units/explicitly_convertible.adoc[`explicitly_convertible`] and is used to validate quantities belonging to the same kind but with otherwise unrelated equations.

== Return Value

`true` if `from` can be cast to `to`

[NOTE]
====
The return value https://en.cppreference.com/cpp/language/attributes/nodiscard[should not be discarded^].
====
== Template Parameters

[cols="1,4"]
|===
| Name| Description
| *From*
| source quantity specification type
| *To*
| target quantity specification type
|===

== Parameters

[cols="1,4"]
|===
| Name| Description
| *from*
| source quantity specification value
| *to*
| target quantity specification value
|===


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