Re: Top level array constness discarding and Variant
On Monday, 30 July 2012 at 20:56:30 UTC, Jonathan M Davis wrote:
On Monday, July 30, 2012 23:44:56 cybevnm wrote:
During initializing Variant, D discards top level const of
array, which
leads to little unintuitive behaviour. Consider code:
import std.stdio;
import std.variant;
void main()
{
const int[] arr;
Variant v = Variant( arr );
writeln( v.peek!( typeof( arr ) )() );
writeln( v.peek!( const(int)[] )() );
writeln( v.type() );
}
...and output:
%dmd main.d ./main.d
null
7FFF358AE298
const(int)[]
As you can see peek works successfully not for original array
type, but
for type without top level const. Is Variant supposed to work
in that way ?
Probably not. When arrays are passed to templated functions,
they're passed as
tail-const (so the constness on the array itself - but not its
elements - is
stripped), which in general is _way_ more useful than passing
them as fully
const. However, Variant predates that behavior by quite a
while, and it's
well-passed due for having extensive work done on its
implementation (it's API
should be fine, but it was implemented when D was much younger,
and we can do a
much better job of it now). There's a discussion on that in the
main newsgroup
at the moment actually.
In any case, please create a bug report for this:
http://d.puremagic.com/issues
- Jonathan M Davis
http://d.puremagic.com/issues/show_bug.cgi?id=8486
Re: Top level array constness discarding and Variant
On Monday, July 30, 2012 23:44:56 cybevnm wrote:
During initializing Variant, D discards top level const of array, which
leads to little unintuitive behaviour. Consider code:
import std.stdio;
import std.variant;
void main()
{
const int[] arr;
Variant v = Variant( arr );
writeln( v.peek!( typeof( arr ) )() );
writeln( v.peek!( const(int)[] )() );
writeln( v.type() );
}
...and output:
%dmd main.d ./main.d
null
7FFF358AE298
const(int)[]
As you can see peek works successfully not for original array type, but
for type without top level const. Is Variant supposed to work in that way ?
Probably not. When arrays are passed to templated functions, they're passed as
tail-const (so the constness on the array itself - but not its elements - is
stripped), which in general is _way_ more useful than passing them as fully
const. However, Variant predates that behavior by quite a while, and it's
well-passed due for having extensive work done on its implementation (it's API
should be fine, but it was implemented when D was much younger, and we can do a
much better job of it now). There's a discussion on that in the main newsgroup
at the moment actually.
In any case, please create a bug report for this:
http://d.puremagic.com/issues
- Jonathan M Davis
