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digitalmars.D.learn - Scalar + array operations

reply "Stefan Frijters" <sfrijters gmail.com> writes:
When working on my current project (writing a numerical 
simulation code) I ran into the following issue when trying to 
multiply a vector (represented by a fixed-length array) by a 
scalar:

import std.stdio;

void main() {
   int ifoo = 2;
   int[3] ibar = 1;

   double dfoo = 2.0;
   double[3] dbar = 1.0;

   dfoo = ifoo * dfoo;      // Scalar int * scalar double -- OK
   writeln(dfoo);
   dfoo = dfoo * dfoo;      // Scalar double * scalar double -- OK
   writeln(dfoo);
   dbar = dfoo * dbar[];    // Scalar double * array of double -- 
OK
   writeln(dbar);
   ibar = ifoo * ibar[];    // Scalar int * array of int -- OK
   writeln(ibar);
   dbar = ifoo * dbar[];    // Scalar int * array of double -- OK
   writeln(dbar);
   // dbar = dfoo * ibar[]; // Scalar double * array of int -- FAIL
   // writeln(dbar);
}

I would have expected the last case to work as well, but I get

testarr.d(20): Error: incompatible types for ((dfoo) * (ibar[])): 
'double' and 'int[]'

Is this by design? It was very surprising to me, especially since 
all other combinations do seem to work.

Kind regards,

Stefan Frijters
May 21 2014
next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
Stefan Frijters:


 Is this by design? It was very surprising to me, especially 
 since all other combinations do seem to work.


I don't know if this situation is by design. At first sights it 
seems a limitation that could be removed.

Bye,
bearophile
May 21 2014
prev sibling parent reply "John Colvin" <john.loughran.colvin gmail.com> writes:
On Wednesday, 21 May 2014 at 11:45:57 UTC, Stefan Frijters wrote:

 When working on my current project (writing a numerical 
 simulation code) I ran into the following issue when trying to 
 multiply a vector (represented by a fixed-length array) by a 
 scalar:

 import std.stdio;

 void main() {
   int ifoo = 2;
   int[3] ibar = 1;

   double dfoo = 2.0;
   double[3] dbar = 1.0;

   dfoo = ifoo * dfoo;      // Scalar int * scalar double -- OK
   writeln(dfoo);
   dfoo = dfoo * dfoo;      // Scalar double * scalar double -- 
 OK
   writeln(dfoo);
   dbar = dfoo * dbar[];    // Scalar double * array of double 
 -- OK
   writeln(dbar);
   ibar = ifoo * ibar[];    // Scalar int * array of int -- OK
   writeln(ibar);
   dbar = ifoo * dbar[];    // Scalar int * array of double -- OK
   writeln(dbar);
   // dbar = dfoo * ibar[]; // Scalar double * array of int -- 
 FAIL
   // writeln(dbar);
 }

 I would have expected the last case to work as well, but I get

 testarr.d(20): Error: incompatible types for ((dfoo) * 
 (ibar[])): 'double' and 'int[]'

 Is this by design? It was very surprising to me, especially 
 since all other combinations do seem to work.

 Kind regards,

 Stefan Frijters


Please file a bug, there's no reason for that not to work, it 
just needs to be implemented properly.
May 21 2014
next sibling parent "Stefan Frijters" <sfrijters gmail.com> writes:
On Wednesday, 21 May 2014 at 13:52:47 UTC, John Colvin wrote:

 Please file a bug, there's no reason for that not to work, it 
 just needs to be implemented properly.


Ok, thanks for confirming. Filed as 
https://issues.dlang.org/show_bug.cgi?id=12780 .
May 21 2014
prev sibling parent reply "Francesco Cattoglio" <francesco.cattoglio gmail.com> writes:
On Wednesday, 21 May 2014 at 13:52:47 UTC, John Colvin wrote:

 On Wednesday, 21 May 2014 at 11:45:57 UTC, Stefan Frijters 
 wrote:

 I would have expected the last case to work as well, but I get

 testarr.d(20): Error: incompatible types for ((dfoo) * 
 (ibar[])): 'double' and 'int[]'

 Is this by design? It was very surprising to me, especially 
 since all other combinations do seem to work.

 Kind regards,

 Stefan Frijters


 Please file a bug, there's no reason for that not to work, it 
 just needs to be implemented properly.


To me, it just feels reasonable that it is not allowed. What 
should be the correct type of the result? int[]? I thought double 
to int conversion was not allowed unless you explicitly asked for 
it.
May 21 2014
parent "Stefan Frijters" <sfrijters gmail.com> writes:
On Wednesday, 21 May 2014 at 17:07:27 UTC, Francesco Cattoglio 
wrote:

 On Wednesday, 21 May 2014 at 13:52:47 UTC, John Colvin wrote:

 On Wednesday, 21 May 2014 at 11:45:57 UTC, Stefan Frijters 
 wrote:

 I would have expected the last case to work as well, but I get

 testarr.d(20): Error: incompatible types for ((dfoo) * 
 (ibar[])): 'double' and 'int[]'

 Is this by design? It was very surprising to me, especially 
 since all other combinations do seem to work.

 Kind regards,

 Stefan Frijters


 Please file a bug, there's no reason for that not to work, it 
 just needs to be implemented properly.


 To me, it just feels reasonable that it is not allowed. What 
 should be the correct type of the result? int[]? I thought 
 double to int conversion was not allowed unless you explicitly 
 asked for it.


No, I expected and desired an array of doubles, implicitly 
converting the array of ints to doubles.
May 21 2014