pub trait Upcast<T> {
    fn upcast(self) -> T;
}

pub trait IntoUsize {
    fn into_usize(self) -> usize;
}

macro_rules! gen_upcast {
    ($from:ty => $into:ty) => {
        impl Upcast<$into> for $from {
            fn upcast(self) -> $into {
                self as $into
            }
        }
    }
}

// Unsigned
gen_upcast!(u8      => u8);
gen_upcast!(u8      => u16);
gen_upcast!(u8      => u32);
gen_upcast!(u8      => u64);
gen_upcast!(u16     => u16);
gen_upcast!(u16     => u32);
gen_upcast!(u16     => u64);
gen_upcast!(u32     => u32);
gen_upcast!(u32     => u64);
gen_upcast!(u64     => u64);

// Signed
gen_upcast!(i8      => i8);
gen_upcast!(i8      => i16);
gen_upcast!(i8      => i32);
gen_upcast!(i8      => i64);
gen_upcast!(i16     => i16);
gen_upcast!(i16     => i32);
gen_upcast!(i16     => i64);
gen_upcast!(i32     => i32);
gen_upcast!(i32     => i64);
gen_upcast!(i64     => i64);

// Pointer Sized

gen_upcast!(u8      => usize);
gen_upcast!(i8      => isize);
gen_upcast!(u16     => usize);
gen_upcast!(i16     => isize);

#[cfg(any(target_pointer_width = "64", target_pointer_width = "32"))]
gen_upcast!(u32     => usize);

#[cfg(any(target_pointer_width = "64", target_pointer_width = "32"))]
gen_upcast!(i32     => isize);

gen_upcast!(isize   => isize);
gen_upcast!(usize   => usize);


impl IntoUsize for usize {
    fn into_usize(self) -> usize { self }
}

impl<T> IntoUsize for *const T {
    fn into_usize(self) -> usize { self as usize }
}

impl<T> IntoUsize for *mut T {
    fn into_usize(self) -> usize { self as usize }
}

impl<T> IntoUsize for &T {
    fn into_usize(self) -> usize { self as *const _ as usize }
}

impl<T> IntoUsize for &mut T {
    fn into_usize(self) -> usize { self as *mut _ as usize }
}