Should .idup simply do nothing for arrays that are already immutable?

[BCS]

Hello dsimcha,

> import std.stdio;
> 
> void main() {
> immutable foo = "FOO";
> immutable bar = foo.idup;
> writeln(foo.ptr, '\t', bar.ptr);
> }
> Output:
> 42C090  97AE40
> Should we define .idup on an already-immutable array to simply do
> nothing?  It seems that there is never any good reason to copy an
> immutable array, and it would avoid the need to either needlessly copy
> an array or explicitly check for immutability in metaprogramming
> situations.
> 

I can think of one case where I would want to force the copy: In template 
code where I've got a mutable or immutable object/array and I want to make 
a modified immutable version of it. 

- idup it
- modify it via casting away the immutability
- never change it again

To do this totally correctly would requiter 2 copies, (original to mutable 
to immutable). The other option would be to make a mutable copy and then 
cast it into an immutable object.