[boost] Re: static sized strings

From: Martin (adrianm_at_[hidden])
Date: 2004-05-25 00:33:40

I have looked at both implementation and got some comments:

1. Both implementations use a size independent base class. I can see the need 
for such a class but don't understand how to use it in the way proposed. The 
base class only implements a few methods so in my view it is more or less 
useless. E.g. a function taking a "base" argument can't iterate or look at the 
string content without converting it to a c-string (so it could just as well 
use a c-string argument). Why not implement the full interface in the base 
class?

2. I couldn't find any background discussion on what non-const operations  
should be allowed on the string. Only the std::string interface is mentioned 
but since the fixed_string is guaranteed to be continuos it makes sense to 
also allow non-const access to the string.
In both versions c_str() is const while data() is const only in the sandbox 
version. I think a const c_str() and non-const data() (as an overload to keep 
the std::string interface) is the way to go.

3. As mentioned in other posts, length is messy and I don't think there are 
any way to safely store the length inside the class. There will always be a 
risk that the non-const operations add/removes a '\0' in the wrong place. One 
solution may be to add something similar to the CString's "ReleaseBuffer()" 
(with a better name) that allows you to force an update of the length after an 
unsafe operation.

And last just an idea I got from the flex_string implementation: Why not allow 
use of the "struct hack" as a performance option. e.g.

template <typename CharT>
class fixed_string_base {
  const size_t capacity_;
  mutable size_t length_; 
  CharT  str_[1];
protected:
  fixed_string_base(size_t n) : capacity_(n), length_(0) {}
  // std::string interface + special fixed_string operations
};
typedef fixed_string_base<char> char_string;
typedef fixed_string_base<wchar_t> wchar_string;

template <size_t n, typename CharT>
class fixed_string : public fixed_string_base<CharT> {
  CharT str_[n];
public:
  fixed_string() : fixed_string_base<CharT>(n) {}
};