const issues and more!

[Steven Schveighoffer]

"Neil Vice" wrote
> I've been experimenting with const et. al. in 2.009 and have encountered 
> some snags which I'll log here. It is quite likely that some of these 
> issues are unrelated to the recent const changes or are things I have 
> misunderstood and I will appreciate any feedback.
>
> Firstly the following simple initialiser fails to compile:
>
>    char[] text = "text";

This is because a string literal is typed as an invariant(char)[].

const(char)[] text = "text";
or
invariant(char)[] text = "text";
or (with phobos)
string text = "text";

should all work.

>
> As far as I can tell there is no way to declare and initialise an array in 
> a single line of code or even copy an array in a single line once 
> declared. The only way I'm aware of to copy an array is as follows:
>
>    char[] text;
>    text.length = "text".length;
>    text[] = "text";

Yeah, as Matti said, you want "text".dup.  There is a good reason for this. 
A string is an array, which is nothing but a pointer and length.  If you 
allow the line:

char[] text = "text";

to compile, then you are free to modify the constant "text"!  For example, 
in D 1.0 this works:

char[] text = "text";
text[0] = 'n';
char[] text2 = "text";
assert(text2 == "next");

These kinds of errors are subtle and hard to find.  This is why you are not 
allowed to have a non-const or invariant pointer to invariant data such as 
string literals.

-Steve