const and phobos string functions

[Reiner Pope]

Regan Heath wrote:
> Kirk McDonald wrote:
>> In this particular case, you could call this mutating form of 
>> tolower() on the buffer returned from read(), and then split it 
>> afterwards (perhaps yielding strings). This makes a certain degree of 
>> logical sense: If you'd wanted to keep the original contents of the 
>> buffer, you'd have to duplicate it at some point anyway. Since you 
>> don't, you can alter it immediately.
> 
> Sure, that solves this particular case.  But, do you agree there is 
> generally a problem, or shall I continue to dream up example cases for 
> you to solve in some other manner :)
> 
>> I submit the following Python idiom: Functions which mutate their 
>> arguments should return nothing. That is:
>>
>> // Return new string
>> string tolower(string);
>> // Mutate argument
>> void tolower(char[]);
>>
>> This rather strictly highlights the difference between char[] and 
>> string, and makes it essentially impossible to mix up library 
>> functions differentiated in this way.
> 
> That's all well and good until you want to write:
> 
> char[] s;
> ...
> foo(tolower(s));
> 
> If you template tolower in the manner I described it's not possible to 
> mix it up and call the wrong one anyway (as it selects the correct one 
> based on the input) so it's a non-problem.
> 
> Regan

I think the code you gave here would be misleading. For instance, 
suppose you had your templated overloads, effectively giving you

    // copy-on-write
    string tolower(string);
    // in-place
    char[] tolower(char[]);

Then you would get surprising results if you did this:

char[] s = "Hello World!".dup;
int a = howManyLettersDiffer(tolower(s), s);
assert (a == 2); // assert failed, a is actually 0

I think avoiding this is exactly why Kirk suggested his overloads.

   -- Reiner