On Sun, 11 Dec 2011 16:34:34 -0500, Jonathan M Davis <jmdavisp...@gmx.com>
wrote:
On Sunday, December 11, 2011 10:34:40 Andrei Alexandrescu wrote:
On 12/11/11 9:46 AM, dsimcha wrote:
> On 12/10/2011 4:47 PM, Andrei Alexandrescu wrote:
>> We decided to fix this issue by automatically shedding the top-level
>> const when passing an array or a pointer by value into a function.
>
> Really silly question: Why not do the same for primitives (int, float,
> char, etc.) or even structs without indirection? I've seen plenty of
> code that blows up when passed an immutable double because it tries to
> mutate its arguments. About 1.5 years ago I fixed a bug like this in
> std.math.pow().
Yes, that would be good to do as well.
Actually, that could be a problem for some stuff. It might be an
acceptable
problem, but it creates a problem nonetheless. What about containers?
You can
have arrays with immutable elements, but if you made it so that
immutable int
and int were the same as far as templates were concerned, then it would
be
impossible to have a container which held immutable elements. How big of
a
problem that is, I don't know, but I'd be concerned about some of the
side
effects.
Another concern would be what would happen with primitives when they're
inside
of arrays. e.g.
void func(T)(T[] arr)
Having T lose its constness would be a big problem here.
T does not lose its constness here. const(U[]) would go to const(U)[],
which would then set T = const(U).
Now, if we're talking only IFTI - such func(cast(immutable int)2)
instantiates
with int and func!(immutable int)(2) still instantiates with immutable
int -
and it's only for primitives by themselves (e.g. func above is
unaffected),
then it likely isn't a problem. But we need to really look at the side
effects
of trying to treat primitives as mutable in templates.
We are talking only IFTI.
Specifically, we are saying, for purposes of implying template parameters
during IFTI, strip all the qualifiers from the pieces passed by value, as
long as it doesn't affect any pieces passed by reference.
I bet doing this one thing would instantly trim at least 10k of bloat from
an executable. I'm looking at you, writeln.
And if you're going to do that with primitives, it also opens up the
question
as to what to do with structs which are value types. Should they be
treated
the same?
Yes.
-Steve
