I'm trying to write a Complex type that works for any floaty thing, but can't really get it

Complex.swift

import Foundation;


protocol Num {
    typealias T;
    class func plus(T, T) -> T;
    class func mul(T, T) -> T;
    class func negate(T) -> T;
    class func sub(T, T) -> T;
}

protocol Floating : Num {
    //typealias T;
    class func pi() -> T;
    class func sin(_ : T) -> T;
    class func cos(_ : T) -> T;
    class func sqrt(_ : T) -> T;
}

func Fcos<A : Floating>(a : A.T) -> A.T {
    return A.cos(a);
}
func Fsin<A : Floating>(a : A.T) -> A.T {
    return A.sin(a);
}
func Fpi<A : Floating>() -> A.T {
    return A.pi();
}
func Fsqrt<A : Floating>(a : A.T) -> A.T {
    return A.sqrt(a);
}


struct Complex<A : Floating>
{
    let re, im : A.T;
    
    // cartesian
    init(re:A.T, im:A.T) {
        self.re = re;
        self.im = im;
    }
    // polar
    init(r : A.T, theta : A.T) {
        // Cannot convert the expression's type from "A.T" to "A.T"
        let e : A.T = Fcos(r);
        // Cannot explicitly specialize a generic function
        let e2 : A.T = Fcos<A>(r);
        // ...
        self.re = A.mul(r, A.cos(theta));
        self.im = A.mul(r, A.sin(theta));
    }
}