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August 31, 2010
Re: std.algorithm move() struct emptying
On 2010-08-31 06:16:17 -0400, bearophile <bearophileHUGS@lycos.com> said:

> If in generic code T.init is not guaranteed to be an lvalue, as your 
> example shows, isn't it better to disallow (turning it into a syntax 
> error) &T.init in all cases?

Personally, I'd say the code should check if T.init is an lvalue using 
__traits(compiles, &T.init) or is(typeof(&T.init)) and avoid creating a 
static variable or temporary when it is. This optimization of course 
depends &T.init not being a syntax error.

-- 
Michel Fortin
michel.fortin@michelf.com
http://michelf.com/
August 31, 2010
Re: std.algorithm move() struct emptying
31.08.2010 16:49, Michel Fortin пишет:
> On 2010-08-31 06:16:17 -0400, bearophile <bearophileHUGS@lycos.com> said:
>
>> If in generic code T.init is not guaranteed to be an lvalue, as your 
>> example shows, isn't it better to disallow (turning it into a syntax 
>> error) &T.init in all cases?
>
> Personally, I'd say the code should check if T.init is an lvalue using 
> __traits(compiles, &T.init) or is(typeof(&T.init)) and avoid creating 
> a static variable or temporary when it is. This optimization of course 
> depends &T.init not being a syntax error.
>
Well, currently there's even nastier thing than syntax error.

struct S
{
int a;
@property static S init() { return S(10); }
}

Or even

struct S
{
@property static void init() {}
}

Personally I agree with bearophile, but maybe the code such as above 
should be forbidden as well, and for other builtin properties too?
August 31, 2010
Re: std.algorithm move() struct emptying
On 8/31/10 7:49 CDT, Michel Fortin wrote:
> On 2010-08-31 06:16:17 -0400, bearophile <bearophileHUGS@lycos.com> said:
>
>> If in generic code T.init is not guaranteed to be an lvalue, as your
>> example shows, isn't it better to disallow (turning it into a syntax
>> error) &T.init in all cases?
>
> Personally, I'd say the code should check if T.init is an lvalue using
> __traits(compiles, &T.init) or is(typeof(&T.init)) and avoid creating a
> static variable or temporary when it is. This optimization of course
> depends &T.init not being a syntax error.

I recall I wrote that code to avoid a compiler bug when T == Tuple!(some 
types).

Andrei
August 31, 2010
Re: std.algorithm move() struct emptying
On Tue, Aug 31, 2010 at 17:05, Andrei Alexandrescu <
SeeWebsiteForEmail@erdani.org> wrote:

> On 8/31/10 7:49 CDT, Michel Fortin wrote:
>
>> On 2010-08-31 06:16:17 -0400, bearophile <bearophileHUGS@lycos.com> said:
>>
>>  If in generic code T.init is not guaranteed to be an lvalue, as your
>>> example shows, isn't it better to disallow (turning it into a syntax
>>> error) &T.init in all cases?
>>>
>>
>> Personally, I'd say the code should check if T.init is an lvalue using
>> __traits(compiles, &T.init) or is(typeof(&T.init)) and avoid creating a
>> static variable or temporary when it is. This optimization of course
>> depends &T.init not being a syntax error.
>>
>
> I recall I wrote that code to avoid a compiler bug when T == Tuple!(some
> types).
>
> Andrei
>

Is that related to this bug?
http://d.puremagic.com/issues/show_bug.cgi?id=4536


Philippe
August 31, 2010
Re: std.algorithm move() struct emptying
On 8/31/10 11:28 CDT, Philippe Sigaud wrote:
> On Tue, Aug 31, 2010 at 17:05, Andrei Alexandrescu
> <SeeWebsiteForEmail@erdani.org <mailto:SeeWebsiteForEmail@erdani.org>>
> wrote:
>
>     On 8/31/10 7:49 CDT, Michel Fortin wrote:
>
>         On 2010-08-31 06:16:17 -0400, bearophile
>         <bearophileHUGS@lycos.com <mailto:bearophileHUGS@lycos.com>> said:
>
>             If in generic code T.init is not guaranteed to be an lvalue,
>             as your
>             example shows, isn't it better to disallow (turning it into
>             a syntax
>             error) &T.init in all cases?
>
>
>         Personally, I'd say the code should check if T.init is an lvalue
>         using
>         __traits(compiles, &T.init) or is(typeof(&T.init)) and avoid
>         creating a
>         static variable or temporary when it is. This optimization of course
>         depends &T.init not being a syntax error.
>
>
>     I recall I wrote that code to avoid a compiler bug when T ==
>     Tuple!(some types).
>
>     Andrei
>
>
> Is that related to this bug?
> http://d.puremagic.com/issues/show_bug.cgi?id=4536
>
>
> Philippe

Very possible.

Andrei
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