const?? When and why? This is ugly!

[Walter Bright]

Derek Parnell wrote:
> On Sat, 07 Mar 2009 14:43:50 -0800, Walter Bright wrote:
> 
>> int foo(const(char)[] s)
>>
>> what if foo() keeps a private reference to s (which it might if it does 
>> lazy evaluation)? Now I, as a caller, mutate s[] and muck up foo. So, to 
>> fix it, I do:
>>
>> foo(s.dup);    // defensive copy in case foo keeps a reference to s
> 
> In foo's defence, if it takes a private reference, then it should also take
> a copy.

Yup, and as I said, an extra copy "just in case".

> In fact, should it be allowed to take a private reference of data
> which might be modified after it returns?
> 

Instead of adding more complexity to const so it acts more like 
immutable, why not just use immutable <g> ?