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digitalmars.D.learn - Why does sum not work in static arrays?

reply Tim K. <invalid webinterface.com> writes:
Hi! I have the following code:

     int main(string[] argv)
     {
         import std.algorithm: sum;
         import std.stdio: writeln;

         uint[3] a1 = [1, 2, 3];
         uint[] a2;
         for (int i = 1; i <= 3; ++i)
             a2 ~= i;

         writeln("a1: ", sum(a1));
         writeln("a2: ", sum(a2));
         return 0;
     }

This throws the error:
dummy.d(11): Error: template std.algorithm.iteration.sum cannot 
deduce function from argument types !()(uint[3]), candidates are:
/usr/include/dmd/phobos/std/algorithm/iteration.d(3916):        
std.algorithm.iteration.sum(R)(R r) if (isInputRange!R && 
!isInfinite!R && is(typeof(r.front + r.front)))
/usr/include/dmd/phobos/std/algorithm/iteration.d(3927):        
std.algorithm.iteration.sum(R, E)(R r, E seed) if (isInputRange!R 
&& !isInfinite!R && is(typeof(seed = seed + r.front)))


So a dynamic array works just fine. In fact, if I uncomment the 
line in question the program compiles and outputs the correct 
value (for a2). Why does "sum" not work on static arrays?


Regards
Dec 06 2015
next sibling parent drug <drug2004 bk.ru> writes:
06.12.2015 15:23, Tim K. пишет:

 Hi! I have the following code:

      int main(string[] argv)
      {
          import std.algorithm: sum;
          import std.stdio: writeln;

          uint[3] a1 = [1, 2, 3];
          uint[] a2;
          for (int i = 1; i <= 3; ++i)
              a2 ~= i;

          writeln("a1: ", sum(a1));
          writeln("a2: ", sum(a2));
          return 0;
      }

 This throws the error:
 dummy.d(11): Error: template std.algorithm.iteration.sum cannot deduce
 function from argument types !()(uint[3]), candidates are:
 /usr/include/dmd/phobos/std/algorithm/iteration.d(3916):
 std.algorithm.iteration.sum(R)(R r) if (isInputRange!R && !isInfinite!R
 && is(typeof(r.front + r.front)))
 /usr/include/dmd/phobos/std/algorithm/iteration.d(3927):
 std.algorithm.iteration.sum(R, E)(R r, E seed) if (isInputRange!R &&
 !isInfinite!R && is(typeof(seed = seed + r.front)))


 So a dynamic array works just fine. In fact, if I uncomment the line in
 question the program compiles and outputs the correct value (for a2).
 Why does "sum" not work on static arrays?


 Regards


Because static array aren't ranges, but dynamic ones are. Try this:
writeln("a1" ", sum (a1[])); // using [] makes static array to be a range
Dec 06 2015
prev sibling parent reply cym13 <cpicard openmailbox.org> writes:
On Sunday, 6 December 2015 at 12:23:05 UTC, Tim K. wrote:

 Hi! I have the following code:

     int main(string[] argv)
     {
         import std.algorithm: sum;
         import std.stdio: writeln;

         uint[3] a1 = [1, 2, 3];
         uint[] a2;
         for (int i = 1; i <= 3; ++i)
             a2 ~= i;

         writeln("a1: ", sum(a1));
         writeln("a2: ", sum(a2));
         return 0;
     }

 This throws the error:
 dummy.d(11): Error: template std.algorithm.iteration.sum cannot 
 deduce function from argument types !()(uint[3]), candidates 
 are:
 /usr/include/dmd/phobos/std/algorithm/iteration.d(3916):        
 std.algorithm.iteration.sum(R)(R r) if (isInputRange!R && 
 !isInfinite!R && is(typeof(r.front + r.front)))
 /usr/include/dmd/phobos/std/algorithm/iteration.d(3927):        
 std.algorithm.iteration.sum(R, E)(R r, E seed) if 
 (isInputRange!R && !isInfinite!R && is(typeof(seed = seed + 
 r.front)))


 So a dynamic array works just fine. In fact, if I uncomment the 
 line in question the program compiles and outputs the correct 
 value (for a2). Why does "sum" not work on static arrays?


 Regards


So that you do not shoot yourself in the foot too easily. A 
static array is a value type so it is passed by value to 
functions. If you pass a 1M array to a function... well, I guesse 
you don't want to do that.

The solution is to slice it:   a1[].sum;   That way you avoid the 
problem.
Dec 06 2015
next sibling parent Tim K. <invalid webinterface.com> writes:
On Sunday, 6 December 2015 at 12:27:49 UTC, cym13 wrote:

 A static array is a value type so it is passed by value to 
 functions.


Oh, right, I totally forgot about that. Thank you for reminding 
me.
And yes, I was not planning on doing that. I just have a local 
fixed-size array that I wanted to get the sum of...


 The solution is to slice it:   a1[].sum;   That way you avoid 
 the problem.


Thank you two.


Regards
Dec 06 2015
prev sibling parent reply mw <mingwu gmail.com> writes:
On Sunday, 6 December 2015 at 12:27:49 UTC, cym13 wrote:

 On Sunday, 6 December 2015 at 12:23:05 UTC, Tim K. wrote:

 Hi! I have the following code:

     int main(string[] argv)
     {
         import std.algorithm: sum;
         import std.stdio: writeln;

         uint[3] a1 = [1, 2, 3];
         uint[] a2;
         for (int i = 1; i <= 3; ++i)
             a2 ~= i;

         writeln("a1: ", sum(a1));
         writeln("a2: ", sum(a2));
         return 0;
     }

 This throws the error:
 dummy.d(11): Error: template std.algorithm.iteration.sum 
 cannot deduce function from argument types !()(uint[3]), 
 candidates are:
 /usr/include/dmd/phobos/std/algorithm/iteration.d(3916):
  std.algorithm.iteration.sum(R)(R r) if (isInputRange!R && 
 !isInfinite!R && is(typeof(r.front + r.front)))
 /usr/include/dmd/phobos/std/algorithm/iteration.d(3927):
  std.algorithm.iteration.sum(R, E)(R r, E seed) if 
 (isInputRange!R && !isInfinite!R && is(typeof(seed = seed + 
 r.front)))


 So a dynamic array works just fine. In fact, if I uncomment 
 the line in question the program compiles and outputs the 
 correct value (for a2). Why does "sum" not work on static 
 arrays?


 Regards


 So that you do not shoot yourself in the foot too easily. A 
 static array is a value type so it is passed by value to 
 functions. If you pass a 1M array to a function... well, I 
 guesse you don't want to do that.


Can the template func `sum()` be made to take `ref` of a static 
array?


 The solution is to slice it:   a1[].sum;   That way you avoid 
 the problem.


While I understand the explanation of the current behavior, and 
the work-around, this inconstancy of making func calls means 
either the library, or the language leaves something to be 
desired: i.e

dynamic array and static array cannot be used interchangeably: 
(sure I'm not talking about array decl / allocation, the user 
have to take different actions) I'm talking about a simple 
function call to calc the sum of the array.
```
   sum(static_array[]);   // v.s.
   sum(dynamic_array);
```

For example, if the user first decl a static array for fast 
prototyping, and later changed mind to use dynamic array, then 
s/he need to change the call all over the places.


(I hope you are not telling me, every time people should use:
```
   array_func(any_array[]);
```
is the correct D-idiom to use array in a func call)
Oct 10 2020
parent reply Alaindevos <devosalain ymail.com> writes:
Sidenote, sort also not works with static arrays.
Oct 11 2020
parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Sun, Oct 11, 2020 at 01:26:13PM +0000, Alaindevos via Digitalmars-d-learn
wrote:

 Sidenote, sort also not works with static arrays.


Just slice it with [].


T

-- 
I think the conspiracy theorists are out to get us...
Oct 11 2020