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Subject: Re: [proto] The proper way to compose function returning expressions
From: Eric Niebler (eric_at_[hidden])
Date: 2012-04-24 16:31:10

On 4/23/2012 10:17 PM, Joel Falcou wrote:
> On 04/24/2012 12:15 AM, Eric Niebler wrote:
>> implicit_expr() returns an object that holds its argument and is
>> convertible to any expression type. The conversion is implemented by
>> trying to implicitly convert all the child expressions, recursively.
>> It sort of worked, but I never worked out all the corner cases, and
>> documenting it would have been a bitch. Perhaps I should take another
>> look. Patches welcome. :-)
> I think this is an important issues to solve as far as Proto grokability
> does.

Agreed. It would be very nice to have. But you still have to know when
to use it.

> One of my coworker on NT2 tried to do just this (the norm2 thingy) and
> he get puzzled by the random crash.
> I think we should at least document the issues (I can write that and
> submit a patch for the doc) and
> maybe resurrect this implicit_expr. Do you have any remnant of code
> lying around so I don't start from scratch ?

The implicit_expr code lived in a detail namespace in past versions of
proto. You can find it if you dig through subversion history. I'm not
going to do that work for you because the code was broken in subtle ways
having to do with the consistency of terminal handling. Repeated
attempts to close the holes just opened new ones. It really should be
left for dead. I'd rather see what you come up with on your own.

Eric Niebler
BoostPro Computing

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