Supported answer: you don't, it has infinite lifetime and
you're claiming it is immutable, but then trying to pull the
memory out from under it! The supported solution is simply to
let the garbage collector manage it.
But..
//GC.free(str_ptr.ptr); // Error: function
core.memory.GC.free (void* p) is not callable using argument
types (immutable(char)*)
If you must call the function though, you can simply
`cast(void*) str.ptr`, or use `char[]` up above instead of
`string` when declaring it, so it has a mutable pointer to
begin with. Since you are using .dup anyway, both declarations
are equally legal.
string str = "aaa";
writeln(str.length); // print 3
str = "bbbb";
writeln(str.length); //print 4 expected 3+4=7 [aaa][bbbb] (2
blocks)
GC.free(cast(void*) str.ptr);
writeln(str.length); //print 4
