[Issue 23375] enum is not considered global mutable state

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23375

Dennis <dkorpel at live.nl> changed:

           What    |Removed                     |Added
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                 CC|                            |dkorpel at live.nl

--- Comment #1 from Dennis <dkorpel at live.nl> ---
I thought it would allocate a new array literal in f(), but it really modifies
global state:

```
class C
{
    string s;
    this(string a) pure @safe nothrow  { s = a; }
    override string toString() {return s;}
}

enum C[] cs = [ new C("a"), new C("b") ];

void f() pure @safe @nogc nothrow
{
    cs[0].s = "c";
}

import std.writeln;
void main()
{
    writeln(cs); // [a, b]
    f();
    writeln(cs); // [c, b]
}
```

I think the could should be accepted without @nogc, and it would modify a copy
of the array.

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