How to declare a memberwise initializer in a Swift extension

SE-0546, a Swift Evolution proposal under review from August 22 through September 4, 2026, would allow a struct's memberwise initializer to be declared in a same-file, unconstrained extension instead of only inside the struct body. Today, a handwritten initializer matching the synthesized signature in an extension is treated as a redeclaration error. Under the proposal, a matching initializer (in labels, types, and order) in a same-file, unconstrained extension would suppress the synthesized one, letting developers raise its access level to public or customize it while keeping stored properties in the main declaration. The proposal covers special cases: failable/throwing initializers suppress the synthesized one, async initializers don't (since Swift can overload on async), constrained extensions don't suppress it, and default parameter values don't affect suppression. This is especially useful for macro-generated public structs, whose synthesized initializers are currently stuck at internal access.

Source: https://sarunw.com/posts/same-file-memberwise-initializer-extensions. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.