[#absl-down_cast-04a]
= xref:absl.adoc[absl]::down_cast
:relfileprefix: ../
:mrdocs:

`down_cast` overloads

== Synopses

Declared in `<absl/base/casts.h>`

Overload of down_cast for references. Use like this: absl::down_cast<T&>(foo). The code is slightly convoluted because we're still using the pointer form of dynamic cast. (The reference form throws an exception if it fails.)


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename To,
    typename From>
[[nodiscard]]
To
xref:absl/down_cast-048.adoc[down_cast](From& f);
----

[.small]#xref:absl/down_cast-048.adoc[_» more..._]#

An "upcast", i.e. a conversion from a pointer to an object to a pointer to a base subobject, always succeeds if the base is unambiguous and accessible, and so it's fine to use implicit_cast.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename To,
    typename From>
[[nodiscard]]
To
xref:absl/down_cast-06.adoc[down_cast](From* f);
----

[.small]#xref:absl/down_cast-06.adoc[_» more..._]#

== Return Value

* `f`, downcast to `To`.
* `f`, downcast to `To`, or null if `f` is null.

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

[cols="1,4"]
|===
| Name| Description
| *f*
| The source reference to downcast.
|===


[.small]#Created with https://www.mrdocs.com[MrDocs]#