[phobos] Pureness of enforce()

[Andrei Alexandrescu]

On 11/12/10 10:21 AM, Steve Schveighoffer wrote:
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>
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> ----- Original Message ----
>> From: Andrei Alexandrescu<andrei at erdani.com>
>> To: Discuss the phobos library for D<phobos at puremagic.com>
>> Sent: Fri, November 12, 2010 12:17:15 PM
>> Subject: Re: [phobos] Pureness of enforce()
>>
>> We should leave enforce() as is and defining eagerEnforce() or
>> pureEnforce().
>>
>> 1. No backwards-incompatible change
>>
>> 2.  enforce() continues to mimic assert()'s behavior wrt its second  argument
>>
>> 3. I'm not sure there will more pure functions than impure out  there. If
>> there are more impure functions, using enforce() becomes a net  pessimization
>>
>> If we make the change, I see "Effective D" item #35:  "Beware of
>> enforce()'s inefficiency".
>
> It's difficult to tell what you mean here by inefficiency -- inefficiency of
> eager version of enforce because the argument is pre-evaluated, or inefficiency
> of lazy version because it cannot be inlined...

The former. I consider the latter a correctable QoI issue.

> In any case, here is the message I wrote about it:
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=115131

To which I replied that I doubt usage inside Phobos is representative. 
Good runtime error messages have been a low (== 0) priority to Phobos. 
In application code I almost always need to construct a string with text().

> I'd say enforce should be the common case, and the common case is that you are
> using constant-folded strings as the argument to enforce.
>
> This almost begs for an 'auto lazy' feature.

Now that would be interesting. By and large, I'd be okay with being able 
to overload on purity.


Andrei