Re: Associative array on the heap
On 7/7/20 3:08 AM, mw wrote:
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)?
AA is a pImpl type wrapper. Yes, it's just a pointer inside.
But it's not simply a pointer because things like indexing can change
the pointer (i.e. if the pointer is null, it will allocate a new AA impl).
If it were just a pointer, then using it without initializing would be a
segfault.
-Steve
Re: Associative array on the heap
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);
Re: Associative array on the heap
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 heap-allocated AA.
But if you wanted to, you could put it in a struct:
struct AA
{
int[string] x;
}
void main()
{
auto b = ((new AA).x);
}
-Steve
Associative array on the heap
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.]
Re: Associative array on the heap
On Tuesday, 19 May 2015 at 00:00:30 UTC, Meta wrote:
On Monday, 18 May 2015 at 23:55:40 UTC, 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.]
They are allocated on the heap implicitly; there's no need for
`new`. You actually *can't* use new with an AA, which is what
the compiler is telling you.
void main()
{
alias A = int[string];
A b = []; //No allocation yet, b is null
b[test] = 1; //b is now non-null
}
Sorry mis-phrased my question,
Who do you allocate a pointer to an associative
array(int[string]*).
Re: Associative array on the heap
On Monday, 18 May 2015 at 23:55:40 UTC, 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.]
They are allocated on the heap implicitly; there's no need for
`new`. You actually *can't* use new with an AA, which is what the
compiler is telling you.
void main()
{
alias A = int[string];
A b = []; //No allocation yet, b is null
b[test] = 1; //b is now non-null
}
Re: Associative array on the heap
On Tuesday, 19 May 2015 at 00:31:50 UTC, Freddy wrote:
Sorry mis-phrased my question,
Who do you allocate a pointer to an associative
array(int[string]*).
Ignoring the why for a moment, one trick is to place it in an
array literal so it's heap allocated. This requires writing an
associative array literal with a single key-element pair though.
int[string]* a = [[zero:0]].ptr;
Another trick is to initially define the associative array in a
class. Since classes are heap allocated, you can allocate an
instance of the class and grab a pointer to the associative array.
class HeapAA
{
int[string] a;
}
int[string]*b = (new HeapAA).a;
Re: Associative array on the heap
On Mon, 18 May 2015 23:55:38 +, 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.]
AAs are always allocated on heap, you don't need to do anything special.
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Re: Associative array on the heap
On Tuesday, 19 May 2015 at 00:00:30 UTC, Meta wrote: A b = []; //No allocation yet, b is null Whoops, you actually can't assign the empty array literal to an AA. This line should be: A b; Which has the exact same effects.
