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digitalmars.D.learn - dupping to allow vector operation?

reply "bearophile" <bearophileHUGS lycos.com> writes:
Observe:

void main() {
      int[3] a1 = [1, 3, 6];
      int[]  a2 = a1[] * 3;       // line 3, Error
      int[]  a3 = a1.dup[] *= 3;  // line 4, OK?
      int[]  a4 = (a1[] * 3).dup; // line 5, Error
}


Currently the operation in line 4 is accepted:

test.d(3,17): Error: array operation a1[] * 3 without destination 
memory not allowed
test.d(5,18): Error: array operation a1[] * 3 without destination 
memory not allowed

Is it a good idea to support something like line 5?

Bye,
bearophile
Oct 09 2014
next sibling parent reply "John Colvin" <john.loughran.colvin gmail.com> writes:
On Thursday, 9 October 2014 at 11:29:14 UTC, bearophile wrote:
 Observe:

 void main() {
      int[3] a1 = [1, 3, 6];
      int[]  a2 = a1[] * 3;       // line 3, Error
      int[]  a3 = a1.dup[] *= 3;  // line 4, OK?
      int[]  a4 = (a1[] * 3).dup; // line 5, Error
 }


 Currently the operation in line 4 is accepted:

 test.d(3,17): Error: array operation a1[] * 3 without 
 destination memory not allowed
 test.d(5,18): Error: array operation a1[] * 3 without 
 destination memory not allowed

 Is it a good idea to support something like line 5?

 Bye,
 bearophile
Why not? Looks fine to me, you've explicitly allocated some new memory for the result to sit in, the lack of which is the motivation for lines 3 an 5 being errors.
Oct 09 2014
parent "John Colvin" <john.loughran.colvin gmail.com> writes:
On Thursday, 9 October 2014 at 18:01:27 UTC, John Colvin wrote:
 On Thursday, 9 October 2014 at 11:29:14 UTC, bearophile wrote:
 Observe:

 void main() {
     int[3] a1 = [1, 3, 6];
     int[]  a2 = a1[] * 3;       // line 3, Error
     int[]  a3 = a1.dup[] *= 3;  // line 4, OK?
     int[]  a4 = (a1[] * 3).dup; // line 5, Error
 }


 Currently the operation in line 4 is accepted:

 test.d(3,17): Error: array operation a1[] * 3 without 
 destination memory not allowed
 test.d(5,18): Error: array operation a1[] * 3 without 
 destination memory not allowed

 Is it a good idea to support something like line 5?

 Bye,
 bearophile
Why not? Looks fine to me, you've explicitly allocated some new memory for the result to sit in, the lack of which is the motivation for lines 3 an 5 being errors.
To clarify: 4 is good, 3 and 5 are not.
Oct 10 2014
prev sibling parent reply "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Thursday, 9 October 2014 at 11:29:14 UTC, bearophile wrote:
 Observe:

 void main() {
      int[3] a1 = [1, 3, 6];
      int[]  a2 = a1[] * 3;       // line 3, Error
      int[]  a3 = a1.dup[] *= 3;  // line 4, OK?
      int[]  a4 = (a1[] * 3).dup; // line 5, Error
 }


 Currently the operation in line 4 is accepted:

 test.d(3,17): Error: array operation a1[] * 3 without 
 destination memory not allowed
 test.d(5,18): Error: array operation a1[] * 3 without 
 destination memory not allowed

 Is it a good idea to support something like line 5?
It's equivalent to: int[] tmp = a1[] * 3; int[] a4 = tmp.dup; The first part is of course identical to line 3, so this should be an error, too. Normal rules for evaluation order require `a1[] * 3` to be evaluated before `(...).dup`, so where is it supposed to store the intermediate result?
Oct 09 2014
parent "bearophile" <bearophileHUGS lycos.com> writes:
Marc Sch├╝tz:

 It's equivalent to:

     int[] tmp = a1[] * 3;
     int[] a4 = tmp.dup;

 The first part is of course identical to line 3, so this should 
 be an error, too. Normal rules for evaluation order require 
 `a1[] * 3` to be evaluated before `(...).dup`, so where is it 
 supposed to store the intermediate result?
So do we need a new different syntax to do it? :-) Bye, bearophile
Oct 09 2014