Does not have witness table for trait

Mojo
1

Earlier the following(or something similar) used to work. I updated to latest mojo and it has started giving me the error listed underneath the code snippet! How can I make this work?

mojo --version => Mojo 25.5.0.dev2025071818 (0b26378c)

@fieldwise_init
struct T(Copyable & Movable):
    alias InnerFn = fn (input: String) escaping -> String
    var inner_fn: UnsafePointer[Self.InnerFn]

    fn __init__(out self):
        self.inner_fn = UnsafePointer[Self.InnerFn]()

    fn do_it(self) -> Self:
        fn some_inner_fn(input: String) escaping -> String:
            return input.upper()

        result = T()
        result.inner_fn = UnsafePointer[Self.InnerFn].alloc(1)
        result.inner_fn.init_pointee_copy(some_inner_fn)
        return result


fn main() raises:
    t = T()
    result = t.do_it()
    from_inner = result.inner_fn[]("here goes my input")

Error:

call expansion failed
        result.inner_fn.init_pointee_copy(some_inner_fn)
        
memory/unsafe_pointer.mojo:1108:56: note: instantiated struct type @"testbed::fn(input: String) escaping -> String" does not have witness table for trait stdlib::builtin::value::Copyable
2

The exact same code works in:

mojo Mojo 25.5.0.dev2025061605 (65500ff8)

Here is the output - HERE GOES MY INPUT

And with mojo Mojo 25.5.0.dev2025071818 (0b26378c) 

unsafe_pointer.mojo:1108:56: note: instantiated struct type @"witness::fn(input: String) escaping -> String" does not have witness table for trait stdlib::builtin::value::Copyable
3

Hi @ratulb, thanks for reporting! Please file an issue on github so we can track this. Thank you!

4

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.