try mojo auto-parameterization (mojo 0.6)

try_auto_paramaterization.mojo

trait Wrappable:
    """
    A nonsensical trait- which can be initialized with an int, or copied.
    """
    fn __init__(inout self, x: Int):
        ...
    fn __copyinit__(inout self, existing: Self):
        ...

@value
struct Wrappee[dtype: DType](Wrappable):
    """
    Implements Wrappable, and stores an int as a SIMD value.
    """
    var value: SIMD[dtype]

    fn __init__(inout self, x: Int):
        self.value = x

    fn __copyinit__(inout self, existing: Self):
        self.value = existing.value

struct Wrapper:
    """
    A struct composed of a Wrappable trait struct.
    """
    var value: Wrappable

    fn __init__(inout self, w: Wrappable):
        self.value = w

fn main():
    let wrappee = Wrappee[DType.float16](3.14)
    let try_wrapper = Wrapper(wrappee)
    # error:         ^ cannot construct 'Wrapper' from 'Wrappee[f16]' value in 'let' initializer