• via Digitalmars-d-bugs (44/44) Aug 31 2014 https://issues.dlang.org/show_bug.cgi?id=13407

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=13407

          Issue ID: 13407
           Summary: Better error message for static array size overflow
           Product: D
           Version: D2
          Hardware: x86
                OS: Windows
            Status: NEW
          Keywords: diagnostic
          Severity: enhancement
          Priority: P1
         Component: DMD
          Assignee: nobody puremagic.com
          Reporter: bearophile_hugs eml.cc

This program:

enum N = 9;
long[1 << N][1 << N][N][N] a;
void main() {}


With dmd 2.067alpha gives the error messages:

test.d(2,28): Error: index 9 overflow for static array
test.d(2,28): Error: index 9 overflow for static array


This means that the array is too much large for a statically allocated array,
but I think the meaning error message is not clear enough. So I suggest
something more similar to (a single error message):

test.d(2,28): Error: array 'a' is too much large (512 * 512 * 9 * 9 of 'long')
to be allocated statically.


In such cases you usually replace the static array with a heap-allocated array,
like:

enum N = 9;
long[][][][] a;
void main() {
    a = new typeof(a)(1 << N, 1 << N, N, N);
}


But this generates a very large number of dynamic arrays that waste time and
efficiency and stress the garbage collector.

So often a better data structure is an array that has dynamic only one or more
of the last coordinates:


enum N = 9;
long[1 << N][1 << N][][] a;
void main() {
    a = new typeof(a)(N, N);
}


Unfortunately I think the error message can't explain this idiom to the user.

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