Why does sum not work in static arrays?
mingwu at gmail.com
Sat Oct 10 19:05:56 UTC 2020
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 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),
>> candidates are:
>> std.algorithm.iteration.sum(R)(R r) if (isInputRange!R &&
>> !isInfinite!R && is(typeof(r.front + r.front)))
>> std.algorithm.iteration.sum(R, E)(R r, E seed) if
>> (isInputRange!R && !isInfinite!R && is(typeof(seed = seed +
>> 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
> 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
> 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
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.
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:
is the correct D-idiom to use array in a func call)
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