https://issues.dlang.org/show_bug.cgi?id=20472

          Issue ID: 20472
           Summary: [REG 2.068] slicing a static array results in another
                    static array
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: wrong-code
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: schveiguy@yahoo.com

If I slice a static array, the type should be a dynamic array:

int[16] x;

pragma(msg, typeof(x[])); // int[]
auto y = x[];
pragma(msg, typeof(y)); // int[]

However, if you slice a static array, and call a template or regular function which accepts a static array that matches the slice size, for some reason the compiler turns it into a static array again:

import std.stdio;

void foo(size_t N)(int[N] arr)
{
    writeln("static: ", N);
}

void foo()(int[] arr)
{
    writeln("dynamic");
}

void main()
{
    int[16] x;
    foo(x);         // static 16
    foo(x[]);       // static 16
    foo(x[0 .. 5]); // static 5 (!)
    auto y = x[];
    foo(y);         // dynamic
}

Note the only way to solve this is to create a new variable. The resulting output should be:

static 16
dynamic
dynamic
dynamic

The end result means workarounds for ensuring you pass a slice and not the entire static array can be overridden by the compiler. This is related to issue 16519, as there's no easy workaround.

run.dlang.io seems to suggest it happened in 2.068.2, someone on the forums suggested PR https://github.com/dlang/dmd/pull/4779

Conversation on forums: https://forum.dlang.org/post/qud5mk$2h9q$1@digitalmars.com

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