[Python-ideas] Special keyword denoting an infinite loop

[Nick Coghlan]

On 28 June 2014 22:53, Devin Jeanpierre <jeanpierreda at gmail.com> wrote:
> On Sat, Jun 28, 2014 at 2:11 AM, Steven D'Aprano <steve at pearwood.info> wrote:
>> On Sat, Jun 28, 2014 at 01:04:24AM -0700, Thomas Allen wrote:
>>> Rust language defines a special way to make an infinite loop (
>>> http://doc.rust-lang.org/tutorial.html#loops).
>>
>> Do they give an explanation for why they use a keyword for such a
>> redundant purpose?
>
> Sure. "while true {...}" would require magic by the compiler to make
> it optimized and to make things like the following pass compile-time
> checks: "let a; while true { a = 1; break;}; return a". With a while
> loop, Rust can't really know that the loop executes even once without
> special-casing the argument, so it emits a compile-time error because
> the variable a might be uninitialized. If Rust magically knew about
> while true, then it becomes confusing if replacing "true" with
> something the compiler doesn't directly understand causes the compiler
> to get confused.
>
> Special cases aren't special enough to break the rules, so Rust
> decides that the special case here deserves its own keyword.

Ah, that makes a lot of sense - I forgot that it wouldn't be just an
optimisation for Rust, but a control flow validity checking change as
well. Thanks for the explanation.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia