There’s nothing special about primitives, they’re just types like any other. A method taking `&mut self` can always modify self, on any type. But you can only call such methods if the value is mutable to begin with, so it’s not really that interesting.

It’s only weird if you come from languages like Java where “primitives” are distinct from “objects”, which is a self-imposed limitation the language imposes.

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Groxx a day ago | parent [-]

Or Go (also treats primitives rather specially) or roughly any language without extension methods (because primitives are at a minimum a pre-defined type). Which is quite a lot of languages really.

Otherwise agreed, methods like this can be mutable in any language that doesn't heavily specialize primitives.

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pjmlp a day ago | parent [-]

Eiffel or Smalltalk are two languages, among others I could chose from, where primitives and others types are differently implemented, yet unless you dive into the nitty gritty details, they look exactly the same to the developer as the compiler handles them exactly the same, and there are no extension methods to be seen.

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kragen 17 hours ago | parent [-]

However, it would be impossible to implement a #toggle method in Smalltalk that behaves like this, because you're calling it on the singleton True (or False) object; Smalltalk local variables, like Lisp variables, are references to objects rather than objects themselves.

(You obviously know this, but it might be a surprise to many people reading this thread.)

	▲	pjmlp 15 hours ago \| parent [-]
		Yes, but that is orthogonal how primitives and reference types get exposed to the developer. Something like toggle is also impossible in languages that favour immutability and forward progress requires creating new variables, like several functional and logic languages.