On Tue, 2016-08-09 at 13:41 -0400, Trevor Saunders wrote:
> If what you want is the ability to put the buffer on the stack
> instead of the heap then I think a stack_string class that
> interoperates with your string class is the thing you want.
I'd avoid a separate stack_string class. Instead use a linear
allocator with storage allocated on the stack, e.g.:
typedef std::basic_string<char, std::char_traits<char>,
linear_allocator<char>
my_tmp_string;
void bleh (int foo)
{
linear_allocator<char> buffer (alloca (1024), 1024);
tmp_string aaa (buffer);
aaa += "test";
aaa += "moon";
...
// what happens when "buffer" runs out of space?
// throw? switch to heap alloc? ...
}
>
> I don't really see anything wrong with a string class being a really
> fancy smart pointer that has a bunch of useful string stuff on it.
That's what std::string basically is?
> As for operator == I'd be fairly ok with that, other than it hiding
> a O(N) operation in ==.
Yes, it makes it more difficult to carry out algorithm complexity
analysis using grep...
> Regretably necessary sure, but I'm not sure its funny.
Hence the quotes.
> The first big problem with using the stl is that the subset available
> in C++98 isn't that great, you could maybe hack up libstdc++ so that
> you can use newer types just without the bits that use newer language
> features, but that would take some work.
Or just wait until people have agreed to switch to C++11 or C++14. I
don't think in practice anybody uses an C++11-incapable GCC to build a
newer GCC these days.
> The other big problem is that the stl is often too general, and tries
> to be too simple. std::string is actually a good example of both of
> those problems. There's really no reason it should use size_t
> instead of uint32_t for the string length / capacity.
Yes, some of the things in the STL are collections of compromises for
general-purpose usage. If you're doing something extra fancy, most
likely you can outperform the generic STL implementation. But very
often it's actually not needed.
> It would also be a lot better if it had separate types for strings
> where you want an internal buffer or don't.
Using custom allocators is one way. For example ...
template <unsigned int BufferSize> struct linear_allocator_with_buffer;
template <unsigned int BufferSize>
using stack_string =
std::basic_string<char, std::char_traits<char>,
linear_allocator_with_buffer<BufferSize>>;
But then ...
stack_string<32> a = "a";
stack_string<64> b = "b";
b += a;
... will not work because they are different types.
One drawback of using custom allocators for that kind of thing is being
unable to pass the above stack_string to a function that takes a "const
std::string&" because they differ in template parameters. But that's
where std::string_view comes in.
Cheers,
Oleg
