Re: dupping to allow vector operation?

[John Colvin via Digitalmars-d-learn]

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.

dupping to allow vector operation?

[bearophile via Digitalmars-d-learn]

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

Re: dupping to allow vector operation?

[John Colvin via Digitalmars-d-learn]

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.

Re: dupping to allow vector operation?

[via Digitalmars-d-learn]

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?

Re: dupping to allow vector operation?

[bearophile via Digitalmars-d-learn]

Marc Schütz:


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