protocol for using InputRanges

[Steven Schveighoffer]

On Thu, 27 Mar 2014 00:17:21 -0400, Walter Bright  
<newshound2 at digitalmars.com> wrote:

> On 3/26/2014 7:55 PM, Steven Schveighoffer wrote:
>> OK, but it's logical to assume you *can* avoid a call to empty if you  
>> know
>> what's going on under the hood, no? Then at that point, you have lost  
>> the
>> requirement -- people will avoid calling empty because they can get  
>> away with
>> it, and then altering the under-the-hood requirements cause code  
>> breakage later.
>>
>> Case in point, the pull request I referenced, the author originally  
>> tried to
>> just use empty to lazily initialize filter, but it failed due to  
>> existing code
>> in phobos that did not call empty on filtered data before processing.  
>> He had to
>> instrument all 3 calls.
>
> As with *any* API, if you look under the hood and make assumptions about  
> the behavior based on a particular implementation, assumptions that are  
> not part of the API, the risk of breakage inevitably follows.

Like range.save. It's "required", but frequently omitted, without any  
consequences. I'm not saying requiring it would be an invalid decision,  
I'm saying requiring it would be a futile gesture -- the requirement would  
be ignored.

What happens when one of our "clients" code breaks severely because we  
make a change in phobos that assumes empty is always called first on a  
newly-created range?

> If you've identified Phobos code that uses ranges but does not follow  
> the protocol, the Phobos code is broken - please file a bugzilla issue  
> on it.

I think we should work on making a protocol that does not require awkward  
calls, rather than alienating developers who don't follow the awkward  
protocol.

BTW, I think there has been recent talk about not focusing on dust when we  
are laying bricks. This would have my vote as useless dust. This does not  
solve the problem of streams-as-ranges, because streams don't make good  
ranges. It doesn't really solve any problems as far as I can tell.

-Steve