Modular•5d ago

List of references in Mojo

I'm a bit out of the loop with the latest Mojo developments, so I could use some guidance. In Python, creating a list of references is simple:

m1 = [1, 2]
m2 = [3, 4]
l = [m1, m2]
l[0][0] = 5
print(m1[0])  # -> 5

m1 = [1, 2]
m2 = [3, 4]
l = [m1, m2]
l[0][0] = 5
print(m1[0])  # -> 5

How would we achieve similar functionality in Mojo nowadays? Is UnsafePointer still the way to go, something like:

from memory import UnsafePointer
fn main():
    var m1 = UnsafePointer[Int].alloc(2)
    var m2 = UnsafePointer[Int].alloc(2)

    m1[0] = 1
    m1[1] = 2
    m2[0] = 3
    m2[1] = 4

    var l = List[UnsafePointer[Int]](capacity=2)
    l.append(m1)
    l.append(m2)

    l[0][0] = 5
    print(m1[0]) # -> 5

from memory import UnsafePointer
fn main():
    var m1 = UnsafePointer[Int].alloc(2)
    var m2 = UnsafePointer[Int].alloc(2)

    m1[0] = 1
    m1[1] = 2
    m2[0] = 3
    m2[1] = 4

    var l = List[UnsafePointer[Int]](capacity=2)
    l.append(m1)
    l.append(m2)

    l[0][0] = 5
    print(m1[0]) # -> 5

Or is there now a more elegant/safer way to achieve this using References? Thx 🙏

6 Replies

Ryulord•5d ago

I think you might just want a List[List[Int]]

Martin Dudek•5d ago

This will copy the lists as far as i see:

fn main():
    var m1 = List[Int](1,2)
    var m2 = List[Int](3,4)
    var l = List[List[Int]](m1,m2)
    l[0][0] = 5
    print(m1[0]) # -> 1

fn main():
    var m1 = List[Int](1,2)
    var m2 = List[Int](3,4)
    var l = List[List[Int]](m1,m2)
    l[0][0] = 5
    print(m1[0]) # -> 1

Ryulord•5d ago

The Reference type is usable but still kinda a pain. Arc is also an option

Martin Dudek•5d ago

It would be great if someone could post how to implement this example with References (and/or Arc) - never used them so not sure how to do it

sora•5d ago

from memory import Arc

fn main():
  l1 = Arc(List(1, 2))
  l2 = Arc(List(3, 4))
  l3 = List(l1, l2)
  l3[0][][0] = 10
  print(l1[].__str__())

from memory import Arc

fn main():
  l1 = Arc(List(1, 2))
  l2 = Arc(List(3, 4))
  l3 = List(l1, l2)
  l3[0][][0] = 10
  print(l1[].__str__())

Martin Dudek•5d ago

this looks great, thanks a lot

Gaming

Programming

List of references in Mojo