Swift 45%, Kotlin 86% — The Numbers Behind Language Bootstrapping

Did you know that Swift is written 45.3% in Swift and Kotlin is written 86.1% in Kotlin?

— No, and what?

That means Swift and Kotlin are bootstrapping themselves.

— Hmm, what do you mean by bootstrapping?

A language is bootstrapping when it can compile its own source code using a previous version of the language’s binary.

— Ok, so Swift and Kotlin are partially bootstrapped. Are there any languages that are 100% bootstrapped?

There are languages with higher percentages of their own language code, but I’d be careful claiming 100% bootstrappability — even if TypeScript shows 99% TypeScript — because language repos often include other tools alongside the compiler.

— Ok, can you list popular languages on GitHub and their bootstrap stats as of today?

Yes, here you go:

• Go — Go 89.5%, Assembly 5.5% — https://github.com/golang/go
• PHP — C 70.1%, PHP 27.6% — https://github.com/php/php-src
• Swift — C++ 46.6%, Swift 45.3% — https://github.com/swiftlang/swift
• V8 (JavaScript) — C++ 72.2%, JavaScript 25.6% — https://github.com/v8/v8
• OpenJDK — Java 73.9%, C++ 14.1% — https://github.com/openjdk/jdk
• CPython — Python 62.3%, C 35.8% — https://github.com/python/cpython
• Kotlin — Kotlin 86.1%, Java 5.5% — https://github.com/JetBrains/kotlin

Boostrapping by the Numbers: How Much Code is Self-Written

— Super info, thanks. Can you email me when Swift and Kotlin increase their bootstrappability?

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