InteropOddities.md

** ‼️ The official C++ interoperability documentation is live at Swift.org and provides an up-to-date guide for mixing Swift and C++ ‼️ **

C++ Interoperability Oddities

C++ APIs may have slightly different behavior than other C++ APIs. This is a general catch-all document where these oddities are recorded along with a few other things that are good to know when using C++ interop.

Parameters with reference types

Parameters that have mutable reference types are bridged as inout. Parameters with immutable reference types (const ref) are bridged as value types. ⚠️ This will change as soon as Swift has a way to represent immutable borrows. ⚠️

Lifetimes

Currently, lifetimes are extended to the end of the lexical scope if any unsafe pointers are used in that scope. TODO: this should be updated to extend lifetimes whenever a C++ type is used in that scope. Currently, if there is no unsafe pointer used in the scope, then normal Swift lifetime rules apply.

Borrowing Self

For mutating methods, self is borrowed and the access to self lasts for the duration of the call. For non-mutating methods, the access to self is currently instantaneous. ⚠️ In the very near future we plan to borrow self in both cases. This will be a source breaking change from what native Swift methods do. ⚠️

More to come soon :)