Fully transitive const is not necessary

[Walter Bright]

Sascha Katzner wrote:
> Correct me if I'm wrong, but if you want to concatenate two invariant 
> strings, you have to allocate a new buffer. Isn't that a possible speed 
> penalty compared to regular strings? Since if you use regular strings 
> you can allocate one of the two string buffers beforehand big enough and 
> save this allocation, with invariant strings you don't have this option.
> 
> ...or to rephrase my question, wouldn't a StringBuilder Class without 
> invariant strings be much faster?

D doesn't *prevent* you from building a string using a mutable character 
array. The cases where it is faster to do so, however, tend to be 
modularizable. When the function is done, the result can be cast to an 
invariant string.