The DIP Process

[H. S. Teoh]

On Tue, Feb 26, 2019 at 06:12:45PM -0700, Jonathan M Davis via Digitalmars-d wrote:
> On Tuesday, February 26, 2019 5:53:51 PM MST Nicholas Wilson via 
> Digitalmars-d wrote:
[...]
> > FWIW Walter has said that if alias this had been proposed today that
> > it would be rejected because it has too many nasty corner cases. I
> > happen to believe alias this is awesome but I do see where he's
> > coming from and I've been reviewing a lot of Razvan's PRs fixing
> > those corner cases so I know they do exist. One of the points on the
> > agenda for the DLF meeting at dconf is a review of the state of
> > alias this.
> 
> It's one of those features that's occasionally useful, but in general,
> I'm inclined to think that it causes way more trouble than it's worth.
> Honestly, implicit conversions in general tend to be problematic much
> as they can be really nice to have sometimes. They're particularly bad
> when templates get involved.
[...]

I'm a pretty heavy user of alias this, and would be quite unhappy if the
present semantics were to change or become deprecated or otherwise cease
being supported.  I understand there are some dark corner cases where
it's not at all obvious what the "correct" behaviour is, but still,
alias this does offer significant value for arithmetical types and
wrapper types.  I'd even say that in many cases, it *helps* with
templates because it lets you make your custom type work with a template
that doesn't (and shouldn't) know about the specifics of your type.

Where it breaks down is when templates are written with assumptions that
don't come directly from introspection.  Then you start getting into
ambiguous corner cases and other nasty unexpected behaviours.

Anyway, if anything were to change with alias this, we'd better have a
darned good replacement for it, because I'll be expecting it!


T

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