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{{#title Function pointers — Rust ♡ C++}}
# Function pointers
### Public API:
```cpp,hidelines=...
// rust/cxx.h
...
...namespace rust {
template <typename Signature>
class Fn;
template <typename Ret, typename... Args>
class Fn<Ret(Args...)> final {
public:
Ret operator()(Args... args) const noexcept;
Fn operator*() const noexcept;
};
...
...} // namespace rust
```
### Restrictions:
Function pointers with a Result return type are not implemented yet.
Passing a function pointer from C++ to Rust is not implemented yet, only from
Rust to an `extern "C++"` function is implemented.
## Example
Function pointers are commonly useful for implementing [async functions over
FFI](../async.md). See the example code on that page.
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