I dont have the answer but i'll participate

https://docs.modular.com/mojo/roadmap.html#the-rebind-builtin

it says: "Mojo cannot always figure out whether some parametric types are equal".." it type-checks the function without instantiation"

so it seems that the rebind function was created for that reason, and not for bitcast conversions

here are some examples:

fn print_int(x:Int):
    print(x)

fn myfunc[T:AnyType](x:T):
    if T == Int: 
        #print_int(x)                #cannot do that because x is still of type T:AnyType
        print_int(rebind[Int](x))   
        
fn main() :
    myfunc[Int](1)

fn myfunc2(x:AnyType):
    print(rebind[Int](x) 1)

fn main() :
    myfunc2(rebind[AnyType](1))

fn print_int(x:Int):
    print(x)

fn myfunc3[T:String](x:AnyType):
    @parameter                       #compile time if statement
    if T == "int_please":
        print_int(rebind[Int](x))
    else:
        print("error..")
    
fn main():
    var x=0
    myfunc3["int_please"](rebind[AnyType](x))
    myfunc3["nothing should happen"](rebind[AnyType](1.4))

parameters cannot be runtime values:
https://docs.modular.com/mojo/programming-manual.html#parameterization-compile-time-metaprogramming

from the page: " We decided to reclaim “parameter” and “parameter expression” to represent a compile-time value in Mojo"

I think that rebind is something for compile time metaprogramming,
maybe your function would work if you return AnyType and accept AnyType, if it is what you try to do,
not to convert a Float to an Int, in the sense of Int(Float(1.1))

Not sure if parameters play a role here. For example, the below code will run, but when you print, it will cause an error.

fn b(num: Int32) -> Float32:
    return rebind[Float32, Int32](num)


b(1)

If i understand the rebind function correctly, it is relabeling the type, not casting

Don't think I am doing anything wrong in my code, I will wait to hear from the Mojo team.

sure, i just felt the need to participate in your issue, you can also come and join the community on discord if you like and have not already 🖖

sure, i just felt the need to participate in your issue

Sure, thanks for your ideas and insights, appreciate your willingness to help 👍

This isn't the intended use of rebind. The rebind builtin doesn't actually do anything -- it asserts that two parametric types are already equal. In your case, you just want a regular cast to Float32 like Float32(num).

I'll improve the error message and update the doc to be clear about its intended usage. Thanks for filing this report!

Ok, sounds good. Probably would be better to rename it too, so as to avoid confusion, as rebind kind of means there is some action happening here. For example in Python, isinstance does a similar thing and is intuitive. Thanks for replying and acting on the report 👍