Writing Pythonic Rust
Over the past several weeks I have been attempting to reimplement the API of an existing python library as a wrapper for an equivalent library in Rust.
tl;dr: this ended up being much harder than I expected it to be, partly because of important differences in the behaviour of the two languages, and partly because of the (self-imposed) obligation to match an existing (idiomatic) python API.
Python is the traditional language of choice for font tools. Popular font editors generally support extensions written in python, and type designers and foundries frequently have extensive collections of scripts and tools for doing font QA, producing proofs, and generating compiled font files.
As we explore writing font tooling in Rust, we would like to be able to continue to support these existing workflows; ideally an existing python script would need only minimal modification in order to continue to work as expected even though the library code it was interacting with would now be written in Rust.
The main challenge faced with this project is working around the fundamental differences between Rust and python, particularly around ownership and mutability. A UFO font object can be thought of as a collection of layers, each of which contains a collection of glyphs, which in turn contain ‘contours’ (bezier paths) and possibly references to other glyphs. Each of these types (Font, Layer, Glyph, Contour, Point) is an object, with reference semantics. This means you can do the following:
