On 14 January 2014 19:04, Manu <turkey...@gmail.com> wrote:
> On 14 January 2014 18:36, Jakob Ovrum <jakobov...@gmail.com> wrote:
>
>> On Tuesday, 14 January 2014 at 08:23:05 UTC, Manu wrote:
>>
>>> 1. A termination condition (ie, while)
>>>
>>> foreach(t; things) iterates each thing, but it's common in traditional
>>> for
>>> loops to have an && in the second 'while' term, to add an additional
>>> termination condition.
>>> for(i=0; i<things.length && things[i].someCondition; ++i)
>>>
>>> Or with foreach:
>>> foreach(i, t; things)
>>> {
>>> if(t.someCondition)
>>> break;
>>> ...
>>> }
>>>
>>
>> foreach(t; things.until!(t => t.someCondition))
>> {
>> }
>>
>> Unfortunately foreach over a range does not automatically support an
>> index loop variable. We could add something like std.range.enumerate to
>> support this, but I think it's a common enough requirement that a language
>> amendment is warranted (there are some subtleties involved in implementing
>> it though - specifically when combined with automatic tuple expansion).
>>
>>
>> 2. A filter
>>>
>>> The other thing is the ability to skip uninteresting elements. This is
>>> typically performed with the first line of the loop testing a condition,
>>> and then continue:
>>> foreach(i, t; things)
>>> {
>>> if(!t.isInteresting)
>>> continue;
>>> ...
>>> }
>>>
>>
>> foreach(t; things.filter!(t => t.isInteresting))
>> {
>> }
>>
>> Ditto about the index loop variable.
>>
>>
>> I've tried to approach the problem with std.algorithm, but I find the
>>> std.algorithm statement to be much more noisy and usually longer when the
>>> loops are sufficiently simple (as they usually are in my case, which is
>>> why
>>> the trivial conditions are so distracting by contrast).
>>>
>>
>> The two examples above look a *lot* cleaner and less noisy (declarative!)
>> to me than the imperative approach using if-break or if-continue.
>
>
> /agree completely.
> This is nice, I didn't think of writing statements like that :)
> That's precisely the sort of suggestion I was hoping for. I'll continue
> like this.
>
Can anyone comment on the codegen when using these statements? Is it
identical to my reference 'if' statement?
Liberal use of loops like this will probably obliterate unoptimised
performance... :/
