trusted purity?

[monarch_dodra]

On Monday, 29 April 2013 at 11:50:11 UTC, Henning Pohl wrote:
> On Monday, 29 April 2013 at 11:32:33 UTC, monarch_dodra wrote:
>> I'm still worried about what it means for a pure function to 
>> throw... (I'm thinking about the  "enforce(malloc)" scheme)
>
> If malloc returns null, we are out of memory. In D this is not 
> an exception, it is an error. So I guess we just need to check 
> the pointer returned by malloc and throw an OutOfMemoryError on 
> failure. Thus if the ctor called is nothrow, it can be marked 
> as nothrow, too.
>
> So in this case, there should be no problem making it pure.

I've hit this issue before: In D, if the *managed* memory runs 
out, then it is an error (since then *everything* crumbles: 
arrays, GC. etc). The reason it is an error is that since the 
memory is managed by the language, there is nothing the user can 
do anyway, so throwing is pointless.

for unmanaged memory, on the otherhand, the user *can* do 
something about it, so throwing is better.

I myself am not sure I 100% agree with this, but that was the 
conclusion last time I tried to transform an malloc=>Exception 
into a malloc=>Error+Nothrow