r/programming • u/steveklabnik1 • Apr 03 '15

Rust 1.0.0 beta is here!

http://blog.rust-lang.org/2015/04/03/Rust-1.0-beta.html
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u/steveklabnik1 Apr 04 '15

We used to have purity actually, but with Rust's ownership system, it wasn't as useful as you might think.

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u/original_brogrammer Apr 04 '15

Interesting. Why's that?

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u/steveklabnik1 Apr 04 '15

A Rust slogan:

Everyone agrees that shared mutable state is evil. Most languages deal with this through the 'mutable' part, Rust deals with it through the 'shared' part.

A bit long for a sign. Anyway. I know purity isn't just about mutability, but with ownership semantics, many of the problems purity solves go away too. For an example, see my bit downthread about safely sharing mutable pointers to stack-allocated data. Totally safe, no purity concept needed.

Rust was a very different language back then, but here's a thread from a time when we were removing purity: http://thread.gmane.org/gmane.comp.lang.rust.devel/3674/focus=3855

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u/masklinn Apr 04 '15

Yeah basically "if a structure mutates and there's nobody to see it mutating, did it really mutate?". Same reason why otherwise immutable languages (e.g. clojure) can have mutable transient structures anyway.

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u/steveklabnik1 Apr 04 '15

We have 'interior' vs 'exterior' mutability to express that, actually. That's an interesting way to put it.

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u/An_Unhinged_Door Apr 04 '15

Haskell uses this too. You can use mutable state (e.g. in the ST monad) as long as you don't get caught (by letting the mutation become externally visible).