Re: opDispatch and compile time parameters

[Timon Gehr via Digitalmars-d]

On 10/19/2015 09:57 PM, Adam D. Ruppe wrote:

On Monday, 19 October 2015 at 19:53:14 UTC, Andrei Alexandrescu wrote:

struct A {
    int[] x = new int[10];
}

void main() {
    import std.stdio;
    A a;
    a.x[1] = 42;
    writeln(a.x);
}

Looks like a bona fide runtime array to me.

It is still in the static data segment. Try this:


struct A {
     int[] x = new int[10];
}

void main() {
     import std.stdio;
     A a;
     a.x[1] = 42;
     writeln(a.x);

     A a2;
     writeln(a2.x);

     assert(a.ptr is a2.ptr); // passes
}


The `new int[10]` is done at compile time and the pointer it produces is
put into the .init for the struct. So the same pointer gets blitted over
to ALL instances of `A`, meaning they alias the same data (until the
slice gets reallocated by append or whatever).

This is the worst part:

class C{
    int[] x=[1,2,3];
}

void main(){
    auto mut=new C;
    auto imm=new immutable(C);
    assert(imm.x[0]==1);
    mut.x[0]=2;
    assert(imm.x[0]==2);
}