parameter deduction in mojo (0.6) without traits

try_auto_paramaterization.mojo

@value
struct Wrappee[dtype: DType = DType.float16]:
    """
    Stores an int as a SIMD value.
    Defaults to float16.
    """
    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[dtype: DType]:
    """
    A struct composed of a Wrappee.
    """
    var value: Wrappee[dtype]

    fn __init__(inout self, w: Wrappee[dtype]):
        self.value = w

fn main():
    # using lower-level API, we definitely want to optionally specify a dtype
    let pi = Wrappee(3.14)
    let more_pi = Wrappee[DType.float64](3.14)

    # using higher level API, want to optionally specify a dtype, but user usually will not want to deal with it.
    let try_wrapper = Wrapper(pi)
    print(try_wrapper.dtype, try_wrapper.value.value)
    let try_wrapper_more = Wrapper(more_pi)
    print(try_wrapper_more.dtype, try_wrapper_more.value.value)

float16 [3.140625, 3.140625, 3.140625, 3.140625, 3.140625, 3.140625, 3.140625, 3.140625]
float64 [3.1400000000000001, 3.1400000000000001]