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 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 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 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. signature.asc Description: PGP signature
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.
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 00:00:30 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 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 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