In this final part of the series, we’ll explore a trick to make the behaviour of a macro depend on whether it’s used as a statement or as part of an expression. Using that, we’ll make the python!{} macro more flexible to allow saving, reusing, and inspecting Python variables.

Have you ever seen the Rust compiler give a Python error? Or better, have you ever seen rust-analyzer complain about Python syntax? In this post, we’ll extend our python!{} macro to make that happen.

In this part, we’ll extend our python!{}-macro to be able to seamlessly use Rust variables in the Python code within. We explore a few options, and implement two alternatives.

Before continuing to extend our python!{} macro in part 2, let’s explore some things in more detail first.

About a year ago, I published a Rust crate called inline-python, which allows you to easily mix some Python into your Rust code using a python!{ .. } macro. In this series, I’ll go through the process of developing this crate from scratch.

In Software for Infrastructure, Bjarne Stroustrup shows a way to use templates to make the C++ compiler aware of the unit of a value (e.g. kilograms, seconds, etc.), such that it can check consistent use and prevent disasters like the well known error at NASA in 1999 caused by mixing incompatible units. In this article, I show how to extend this idea to support any number of base units and linearly related units (e.g. centimetres, metres and inches) by teaching the compiler how to do arithmetic on units.

Recently, gcc added support rvalue references for *this. (Clang has supported it for quite a while now.) In this post, I show how to use this feature, and how it means we can finally define accessors and a few other things like operator= correctly.