Re: The "=" operator and context
On 3 April 2012 20:38, Moritz Lenz wrote: > which version of Rakudo are you using? (I've tried on the last > development version from git) Rakudo Star 2012.02 % perl6 --version This is perl6 version 2012.02 built on parrot 4.1.0 revision 0 >> Hmm... So you'd have to mess with the STORE method of *all* scalars >> (i.e. not just the Vector() class) ? > > No. Just those that you want to behave specially. And I never > recommended it. Ok. Cheers, Daniel. -- I'm not overweight, I'm undertall.
Re: The "=" operator and context
On 04/03/2012 08:24 PM, Daniel Carrera wrote: > On 3 April 2012 17:24, Moritz Lenz wrote: >> You can, very nearly. You just need to write >> >> my @vec is Vector; >> >> because you really want to change the type of the container, not just of the >> contents (my Vector @vec would be an array containing Vector objects). > > > Another option might be to just use scalar variables to hold vectors: > > my Vector $vector; > my Vector @array_of_vectors; > > $vector = 1,2,3,4,5; but then you don't get list assignment semantics for that last line, so it'll parse as ($vector = 1), 2, 3, 4, 5; > Doesn't work for me :-( For me the last statement gives "12". which version of Rakudo are you using? (I've tried on the last development version from git) > >> (you can also override the .STORE method of a scalar, but that's a bit >> creepy if you ask me). > > Hmm... So you'd have to mess with the STORE method of *all* scalars > (i.e. not just the Vector() class) ? No. Just those that you want to behave specially. And I never recommended it. Cheers, Moritz
Re: The "=" operator and context
On 3 April 2012 17:24, Moritz Lenz wrote:
> You can, very nearly. You just need to write
>
> my @vec is Vector;
>
> because you really want to change the type of the container, not just of the
> contents (my Vector @vec would be an array containing Vector objects).
Another option might be to just use scalar variables to hold vectors:
my Vector $vector;
my Vector @array_of_vectors;
$vector = 1,2,3,4,5;
> class Vector is Array {}
> multi sub infix:<*>(Vector $a, Real $b) {
> Vector.new( $a.list X* $b );
> }
>
> my @vec := Vector.new(1, 2, 3, 4);
> say @vec.WHAT;
> say @vec * 3;
>
> Output:
>
> Vector()
> 3 6 9 12
>
> Using binding := instead of assignment replaces the array container with a
> Vector object.
Doesn't work for me :-( For me the last statement gives "12".
> (you can also override the .STORE method of a scalar, but that's a bit
> creepy if you ask me).
Hmm... So you'd have to mess with the STORE method of *all* scalars
(i.e. not just the Vector() class) ?
Daniel.
--
I'm not overweight, I'm undertall.
Re: The "=" operator and context
Am 03.04.2012 17:10, schrieb Daniel Carrera:
(1..10).WHAT # => Range()
@foo = 1..10;
@foo.WHAT # => Array()
When you assign a range to @foo, the result is an array. Something
similar happens, for example, if you assign a scalar to @foo... The
context of the assignment causes Perl 6 to convert the value into an
array.
I was wondering if this sort of magic is limited to pre-defined types
(arrays, hashes, etc) or if it can be extended to any class that I
might create.
It's something inbetween. The distinction between the list assignment
and scalar assignment is syntactic. In the case of list assignment,
@foo.STORE(1..10) is called under the hood.
For example, imagine hat I create a 'Vector' class to do
basic linear algebra. Imagine that it works this way:
my @vec = Vector.new( 1,2,3,4 )
@vec * 3 # => ( 3,6,9,12 )
In other words, the '*' operator is overloaded to behave like scalar x
vector multiplication in linear algebra. I was thinking that it would
be neat if instead you could do this:
my Vector @vec;
@vec = 1,2,3,4;
@vec.WHAT # => Vector()
You can, very nearly. You just need to write
my @vec is Vector;
because you really want to change the type of the container, not just of
the contents (my Vector @vec would be an array containing Vector objects).
This syntax doesn't quite work yet in Rakudo (though it wouldn't be too
hard to get running), but this works:
use v6;
class Vector is Array {}
multi sub infix:<*>(Vector $a, Real $b) {
Vector.new( $a.list X* $b );
}
my @vec := Vector.new(1, 2, 3, 4);
say @vec.WHAT;
say @vec * 3;
Output:
Vector()
3 6 9 12
Using binding := instead of assignment replaces the array container with
a Vector object.
You can even write
my @vec := Vector.new;
@vec = 1, 2, 3, 4;
and get the same output.
(you can also override the .STORE method of a scalar, but that's a bit
creepy if you ask me).
Cheers,
Moritz
