How I can create a simple basic singleton?

Question

My intention was to create a singleton, but do not know how to handle this in Rust, I have read this and this, but not sure if that's the way to create a simple singleton because one speaks of a "mutable singleton" and the other of a "safe-static-singleton".

I ask this question because in the previous did not explain well, and already has an answer, so I do this and delete the update of the other, to accept the answer without update — Angel Angel
– Angel Angel, Commented Apr 1, 2016 at 19:29
Simple answer would be: you don't. It is almost never good idea to use singletons. — Hauleth
– Hauleth, Commented Apr 1, 2016 at 19:34
Please describe what you want to do with the singleton. If you aren't mutating something, then there are other options. — Shepmaster
– Shepmaster, Commented Apr 1, 2016 at 19:35
@Shepmaster is not anything in particular, I'm creating things I use in other language, to learn something of Rust. Not mutate, just that it always returns the same instance of the object — Angel Angel
– Angel Angel, Commented Apr 1, 2016 at 19:39
I'd warn against blindly copying concepts from other languages as you are less likely to discover the things that make a language unique and useful. Anyway, it sounds like you want a constant of some kind. Follow the instructions to use lazy-static in this answer and just skip the wrapping Mutex. — Shepmaster
– Shepmaster, Commented Apr 1, 2016 at 21:52

Veedrac · Accepted Answer · 2016-04-02 10:29:01Z

6

A singleton is just a lazily initialized piece of static data. That means you really do want lazy-static.

Note that

For a given static ref NAME: TYPE = EXPR;, the macro generates a unique type that implements Deref<TYPE> and stores it in a static with name NAME.

which means NAME is actually akin to the constructor of the "singleton", and &*NAME is the "singleton" itself.

answered Apr 2, 2016 at 10:29

Veedrac

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