On Tuesday, 19 May 2015 at 12:21:48 UTC, Steven Schveighoffer
wrote:
On 5/18/15 7:55 PM, Freddy wrote:
How do you allocate an associative array on the heap?
----
void main(){
alias A=int[string];
auto b=new A;
}
----
$ rdmd test
test.d(4): Error: new can only create structs, dynamic arrays
or class
objects, not int[string]'s
Failed: ["dmd", "-v", "-o-", "test.d", "-I."]
As others have said, I don't know why you would want to do
this, since AA is already simply a wrapper for a pointer to a
AA is a wrapper for a pointer (e.g a struct with some extra info
beyond the plain pointer), or AA is just the plain pointer
(nothing extra)?
I tried this:
class Foo {}
Foo[string] foos;
writeln(foos.sizeof); // print 8
looks like it's just a plain pointer?
The usage pattern to have AA on the heap is, e.g:
class Class {
StudentInfo[string] students; // dict-by-name
// many other fields
}
suppose in a multi-threaded app, the Class object is shared, and
one thread will perform a lengthy updates on all the students. To
ensure data consistency among all the students object, instead of
updating each student's info of the original AA in a loop (with
lengthy locking period), it can be achieved by heap-alloc a new
AA, update the new AA, and atomic-set:
new_students = new StudentInfo[string]; // heap-alloc a new AA
// length update on each of new_students
atomicStore(theClass.students, new_students);
