Against enforce()

[Steven Schveighoffer]

On Thu, 17 Mar 2011 13:30:21 -0400, Simen kjaeraas  
<simen.kjaras at gmail.com> wrote:

> On Thu, 17 Mar 2011 18:17:08 +0100, Steven Schveighoffer  
> <schveiguy at yahoo.com> wrote:
>
>> On Thu, 17 Mar 2011 12:09:50 -0400, bearophile  
>> <bearophileHUGS at lycos.com> wrote:
>>
>>> Steven Schveighoffer:
>>>
>>>> The only problem I see with it is the inline-killing.
>>>
>>> Please don't ignore the purity-killing :-)
>>
>> I think this is not as much an easy fix.  By changing one line in  
>> enforce, every instance becomes inlinable.  By making enforce also  
>> pure, it doesn't automatically make all users of enforce pure.
>>
>> I thought that lazy enforce cannot be pure, but I realize now that it  
>> can, as long as the delegate is pure.  However, I think the compiler  
>> won't cooperate with that.
>
> Not currently, at least. This made me wonder. A delegate created inside a
> pure function would have to be pure while in the scope of that function,
> right? Seems to me that should be possible to implement.

As long as the delegate does not access shared/global data, it should be  
able to be pure.  Even delegates which modify TLS data should be able to  
be pure (weak-pure, but still pure).

This should be easy to enforce when the delegate is created automatically  
 from an expression using a lazy call.  However, we need some implicit  
casting rules for pure delegates into non-pure ones.

-Steve