const issues and more!

[Steven Schveighoffer]

"Bill Baxter" wrote
> Walter Bright wrote:
>> Neil Vice wrote:
>>> Firstly the following simple initialiser fails to compile:
>>>
>>>     char[] text = "text";
>>>
>>> As far as I can tell there is no way to declare and initialise an array 
>>> in a single line of code
>>
>>     string text = "text";
>
> My intuition is that an implicit dup should happen.
> Why?  Well, maybe it's just familiarity with C++?
>
>   std::string text = "hello"; // makes a copy
>   text[0] = 'b'; // ok because we have a copy
>
> --bb

If assigning one string to another made a copy, you lose all the performance 
benefits of slicing.  If I make 20 "copies" of the same string, as long as 
the string is invariant, there is no reason that I need to keep 20 copies of 
it in memory.

That being said, let's examine the following line:

char[] text = "hello";

The compiler could interpret this 2 ways.  One is "yes, compiler, I know 
that "hello" is invariant, I just want a mutable copy of it", The other is 
"oops, I really meant to get a read-only pointer to that string data, so 
give me an error".

If the compiler interprets the first way, the coder who wants a read-only 
pointer isn't warned that he now has used inefficient heap memory.  If the 
compiler inteprets the second way, the coder who wants a copy is told he 
cannot do it that way, he fixes it, and now everyone is happy.

I like the way it works now.  Err on the side of clarity and efficiency.

-Steve