What is Swift written in?
Swift is a general-purpose, multi-paradigm, compiled programming language, first released in 2014.
Implementation
| Layer | Written in | Notes |
|---|---|---|
| Compiler | C (since 2014) | Early Swift compiler had significant C components |
| Compiler | C++ (since 2014) | Swift compiler primarily in C++ |
| Compiler | Swift (since 2019) | Swift compiler increasingly written in Swift |
| Bootstrap | Machine Code (since 2022) | Swift bootstrap chain via LLVM |
| Compiler | LLVM (since 2014) | Swift uses LLVM as compiler backend |
Self-hosting
Swift is a self-hosting language: its compiler is written in Swift itself. Self-hosting means the compiler can compile its own source code, which is a milestone in a language's maturity. New versions of the compiler are built using an older version of the same compiler, a process called bootstrapping.
Self-hosting also acts as a practical stress test: if a language can compile its own compiler, most core language features have been validated in a complex, real-world workload. See what is compiler bootstrapping for a full explanation.
Explore in the Graph
See Swift's full lineage, including all implementation and influence relationships, in the interactive graph.
Open Interactive Graph →Or view the Swift language page for the complete record.