Modular•4w ago

Struct containing a list of itself?

Hi, I'm trying to creating a node-like tree which can contain a child (or children), but the mojo compiler doesn't really let me do that:

@value 
struct Node:
    var value: Int
    var children: List[Node]  # A list of Node objects

    fn __init__(inout self, value: Int):
        self.value = value
        self.children = List[Node]()  # Initialize an empty list

    fn add_child(inout self, child: Node):
        self.children.append(child)  # Add a child node to the list

fn main():
    var root = Node(1)
    var child1 = Node(2)
    var child2 = Node(3)

    root.add_child(child1)
    root.add_child(child2)

    print(root.value)  # Output: 1

@value 
struct Node:
    var value: Int
    var children: List[Node]  # A list of Node objects

    fn __init__(inout self, value: Int):
        self.value = value
        self.children = List[Node]()  # Initialize an empty list

    fn add_child(inout self, child: Node):
        self.children.append(child)  # Add a child node to the list

fn main():
    var root = Node(1)
    var child1 = Node(2)
    var child2 = Node(3)

    root.add_child(child1)
    root.add_child(child2)

    print(root.value)  # Output: 1

error: function has recursive call to 'always_inline' function struct Node: ^ Mojo/USL/shaderlab/libutils/utils_methods.mojo:87:8: note: through call here /Users/ec2-user/actions-runner/_work/modular/modular/Kernels/mojo/stdlib/collections/list.mojo:186:8: note: to function marked 'always_inline' here /Users/ec2-user/actions-runner/_work/modular/modular/Kernels/mojo/stdlib/memory/unsafe_pointer.mojo:413:9: note: call here recurses Mojo/USL/shaderlab/libutils/utils_methods.mojo:87:8: note: back to function here struct Node: ^ mojo: error: failed to run the pass manager

2 Replies

toasty•4w ago

Try list[arc[self]] instead, that’s what I use for a CLI library!

bpr•4w ago

I just compiled and ran your code on nightly and it worked. My Rust instincts are aligned with @toasty, and I thought you'd need to ensure you had a reference to the Node type.

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Struct containing a list of itself?