{{#title Built-in bindings — Rust ♡ C++}}
# Built-in bindings reference

In addition to all the primitive types (i32 <=> int32_t), the following
common types may be used in the fields of shared structs and the arguments and
returns of extern functions.





name in Rust
name in C++
restrictions
String
rust::String

&str
rust::Str

&[T]
rust::Slice<const T>
cannot hold opaque C++ type
&mut [T]
rust::Slice<T>
cannot hold opaque C++ type
CxxString
std::string
cannot be passed by value
Box<T>
rust::Box<T>
cannot hold opaque C++ type
UniquePtr<T>
std::unique_ptr<T>
cannot hold opaque Rust type
SharedPtr<T>
std::shared_ptr<T>
cannot hold opaque Rust type
[T; N]
std::array<T, N>
cannot hold opaque C++ type
Vec<T>
rust::Vec<T>
cannot hold opaque C++ type
CxxVector<T>
std::vector<T>
cannot be passed by value, cannot hold opaque Rust type
*mut T, *const T
T*, const T*
fn with a raw pointer argument must be declared unsafe to call
fn(T, U) -> V
rust::Fn<V(T, U)>
only passing from Rust to C++ is implemented so far
Result<T>
throw/catch
allowed as return type only





The C++ API of the `rust` namespace is defined by the *include/cxx.h* file in
the CXX GitHub repo. You will need to include this header in your C++ code when
working with those types. **When using Cargo and the cxx-build crate, the header
is made available to you at `#include "rust/cxx.h"`.**

The `rust` namespace additionally provides lowercase type aliases of all the
types mentioned in the table, for use in codebases preferring that style. For
example `rust::String`, `rust::Vec` may alternatively be written `rust::string`,
`rust::vec` etc.

## Pending bindings

The following types are intended to be supported "soon" but are just not
implemented yet. I don't expect any of these to be hard to make work but it's a
matter of designing a nice API for each in its non-native language.





name in Rust
name in C++
BTreeMap<K, V>
tbd
HashMap<K, V>
tbd
Arc<T>
tbd
Option<T>
tbd
tbd
std::map<K, V>
tbd
std::unordered_map<K, V>