What can you "new"

[Derek Parnell]

On Sun, 22 Mar 2009 14:31:07 -0400, Steve Teale wrote:

> void str()
> {
>    auto s = new char[];
> }
> 
> void main()
> {
>    str();
> }
> 
> produces:
> 
> str.d(3): Error: new can only create structs, dynamic arrays or class objects, not char[]'s.
> 
> What am I missing here, isn't char[] a dynamic array?

I believe that the message is wrong, or at least misleading. The 'dynamic'
here does not mean variable-length arrays but not 'static' - as in ...
address is not known at compile time.

The 'new' is supposed to create something on the heap and return a
pointer/reference to it. Thus structs, fix-length arrays, and class objects
are obvious candidates for that. Variable-length arrays are always created
on the heap anyway, so to ask for a 'new char[]' is asking for the 8-byte
pseudo-struct for the array to be created on the heap (which would not be
initialized to anything) and return a pointer to it. This would give you
one more level of indirection that you're probably not expecting.

The normal way to create an empty (new, as in never been used yet) char[]
is simply ...

 void str()
 {
    char[] s;
 }
 
But you knew (no pun intended) that already.


What you were actually asking for is more like ...

struct dynary
{
	size_t len;
	void *data;
}

void str()
{
   auto s = cast(char[]*)(new dynary);
}

void main()
{
   str();
}

-- 
Derek Parnell
Melbourne, Australia
skype: derek.j.parnell