Proposal: Relax rules for 'pure'
Jason House
jason.james.house at gmail.com
Fri Sep 24 19:53:47 PDT 2010
Don Wrote:
> Don wrote:
> > The docs currently state that:
>
> > PROPOSAL:
> > Drop the first requirement. Only one requirement is necessary:
> >
> > A pure function does not read or write any global mutable state.
> >
>
> Wow. It seems that not one person who has responded so far has
> understood this proposal! I'll try again. Under this proposal:
>
> If you see a function which has mutable parameters, but is marked as
> 'pure', you can only conclude that it doesn't use global variables.
> That's not much use on it's own. Let's call this a 'weakly-pure' function.
>
> However, if you see a function maked as 'pure', which also has only
> immutable parameters, you have the same guarantee which 'pure' gives us
> as the moment. Let's call this a 'strongly-pure' function.
>
> The benefit of the relaxed rule is that a strongly-pure function can
> call a weakly-pure functions, while remaining strongly-pure.
> This allows very many more functions to become strongly pure.
>
> The point of the proposal is *not* to provide the weak guarantee. It is
> to provide the strong guarantee in more situations.
It looks like your proposal was accepted. Walter just checked in changes to make this a reality. http://www.dsource.org/projects/dmd/changeset/687
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