[Issue 10950] [CTFE] enum "char[]" not correctly duplicated when used.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10950



--- Comment #6 from monarchdodra at gmail.com 2013-09-04 02:00:40 PDT ---
(In reply to comment #5)
> You seem to be expecting the .dup to act as a macro, and be automatically
> applied to any code that uses the enum?

No, not at all.

I expect that when I use CTFE that evaluates a function to initialize an enum,
for it work correctly.

> None of your test cases should compile.

Should this compile?

//----
import std.exception;

string getString()
{
    char[] s = ['a', 'b'];
    return assumeUnique(s);
}
enum string myString = getString();

char[] getArray()
{
  string s = "hello";
  return s.dup;
}
enum char[] myArray = getArray();

unittest
{
  //myString is a string enum, so there should be no allocation.
  string a = myString;
  string b = myString;
  assert(a is b); //This fails. It shouldn't.
}
unittest
{
  //myArray is a char[], so these should allocate.
  char[] a = myArray;
  char[] b = myArray;
  assert(a !is b); //This fails. It shouldn't.
}
//----

Such usage is used extensively throughout phobos. In particular, things like:

enum someString = format(XXXXXXXXX);

If this is not valid code, then I am *completely* lost.

It turns out that when doing this, using "someString" will trigger an
allocation on every use, which is contrary to the whole "string literals don't
allocate". Unless I'm missing something, "someString" *is* a string literal,
right?

The second useage is rarer, but the consequences of the failure are more
problematic (mutables referencing shared immutable data).

I didn't fully understand 4397, but it does look like it's root issue.

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