On Friday, 12 April 2013 at 07:04:23 UTC, Manu wrote:

string[string] is used in the main API to receive environment variables;
perhaps kinda convenient, but it's impossible to supply environment
variables with loads of allocations.

Environment variables are a mapping of strings to strings.  The natural way to express such a mapping in D is with a string[string].  It shouldn't be necessary to allocate an AA literal, though.

toStringz is used liberally; alternatively, alloca() could allocate the
c-string's on the stack and zero terminate them there, passing a pointer to
the stack string to the OS functions.

It is kind of hard to use alloca() in a safe manner in D, because DMD will happily inline functions that use it.  The following program will overflow the stack if compiled with -inline:

void doStuff()
{
    auto p = alloca(100);
}

void main()
{
    foreach (i; 0 .. 1_000_000) doStuff();
}

This is of course fixable, but until that happens, I would consider alloca() a no-go for Phobos.