Why I (Still) Won't Use D

[Janice Caron]

On 28/03/2008, Sean Kelly <sean at invisibleduck.org> wrote:
> I'm sorry, but unless I missed a memo, this hasn't been the case for probably
>  ten years.

In Microsoft's implementation of std::string, there is a one-byte
reference count immediately preceeding the first char. So if you do

    std::string s = "hello";

then somewhere in memory (in fact, at (&s[0])-1), there will be an
array [ 1, 'h', 'e', 'l', 'l', 'o', 0 ], If you then do

    std::string t = s;

then that array changes to [ 2,  'h', 'e', 'l', 'l', 'o', 0 ], but no
copy of the string data is made. If you then modify one of the strings

    s[0] = 'j';

then a new array is constructed, pointers are moved about, counters
are decremented, and you end up with s having an array of [ 1, 'j',
'e', 'l', 'l', 'o', 0 ] and t having a brand new array of [ 1, 'h',
'e', 'l', 'l', 'o', 0 ].

The process stops when the reference counter reaches 254. A value of
255 is special, and means "always copy". Also, these things contain a
lock to keep them thread-safe.

I'm sure that's how it works - at least in Visual Studio 6 and 7. But
feel free to tell me if I'm wrong.