I have a problem with what i think is a corrupted pointer. I have a struct with some_value which I’m trying to access in the iterators next function. But the value becomes a totally scrambled, but only when i get the iterator from the query() function it seems. I have no idea what’s going on here.
Sorry for the lengthy code snippets but i think it might be required to understand where my mistakes are.
Struct with some value:
const Archetype = @This();
some_value: usize = 0,
pub fn query(self: *Archetype, comptime Q: type) q.QueryIterator(Q) {
var iterator = ArchtypeQueryIterator(Q).create(self);
return iterator.iterator();
}
Query iterator interface:
pub fn QueryIterator(comptime Q: type) type {
return struct {
const Self = @This();
pub const VTable = struct {
next: *const fn (ctx: *anyopaque) ?QueryReturnType(Q),
};
ptr: *anyopaque,
vtable: *const VTable,
pub fn next(self: *Self) ?QueryReturnType(Q) {
return self.vtable.next(self.ptr);
}
};
}
Interface implementation whit some prints for debugging.
When i call iterator() to create the iterator the debug prints: “iterator some_value 0” as it should. I also put _ = next(ptr) here for testing and then it always prints “next some value 0” as it should,
pub fn ArchtypeQueryIterator(comptime Q: type) type {
return struct {
const Self = @This();
archetype: *Archetype,
cursor: usize = 0,
pub fn create(archetype: *Archetype) Self {
return .{ .archetype = archetype };
}
pub fn iterator(self: *Self) q.QueryIterator(Q) {
const ptr: *anyopaque = @ptrCast(@alignCast(self));
// prints some_value 0 correctly
std.debug.print("\niterator some_value {}\n", .{self.archetype.some_value});
// When next is called called here some_value prints 0 correctly
_ = next(ptr);
return .{
.ptr = self,
.vtable = &.{
.next = next,
},
};
}
pub fn next(ctx: *anyopaque) ?q.QueryReturnType(Q) {
const self: *Self = @ptrCast(@alignCast(ctx));
std.debug.print("\nnext some_value {}", .{self.archetype.some_value});
return null;
}
};
}
When i call the iterator like this which is what i intend the usage to be, the print from `ǹext()`` becomes some random number.
test "sometest" {
var archetype = try Archetype.init(B1, allocator);
defer archetype.deinit();
// ...
var query_iter = archetype.query(qry);
// When next is called from here some_value returns some random value, corrupted ptr?
_ = query_iter.next();
}
// print looks like this:
// iterator some_value 0
// next some_value 0
// next some_value 356482285568
But if i create the iterator like this, the print becomes some_value 0 as it should.
test "sometest" {
var archetype = try Archetype.init(B1, allocator);
defer archetype.deinit();
// ...
var iterator = ArchtypeQueryIterator(qry).create(&archetype);
var query_iter = iterator.iterator();
// When next is called here it some_value prints 0 correctly
_ = query_iter.next();
}
// print looks like this:
// iterator some_value 0
// next some_value 0
// next some_value 0
