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```
```use num::Zero;
use num_complex::Complex;
#[cfg(feature = "decimal")]
use decimal::d128;

/// Nested sets and conversions between them (using an injective mapping). Useful to work with
/// substructures. In generic code, it is preferable to use `SupersetOf` as trait bound whenever
/// possible instead of `SubsetOf` (because SupersetOf is automatically implemented whenever
/// `SubsetOf` is).
///
/// The notion of "nested sets" is very broad and applies to what the types are _supposed to
/// represent_, independently from their actual implementation details and limitations. For
/// example:
/// * f32 and f64 are both supposed to represent reals and are thus considered equal (even if in
/// practice f64 has more elements).
/// * u32 and i8 are respectively supposed to represent natural and relative numbers. Thus, u32 is
/// a subset of i8.
/// * A quaterion and a 3x3 orthogonal matrix with unit determinant are both sets of rotations.
/// They can thus be considered equal.
///
/// In other words, implementation details due to machine limitations are ignored (otherwise we
/// could not even, e.g., convert a u64 to an i64). If considering those limintations are
/// important, other crates allowing you to query the limitations of given types should be used.
pub trait SubsetOf<T>: Sized {
/// The inclusion map: converts `self` to the equivalent element of its superset.
fn to_superset(&self) -> T;

/// The inverse inclusion map: attempts to construct `self` from the equivalent element of its
/// superset.
///
/// Must return `None` if `element` has no equivalent in `Self`.
fn from_superset(element: &T) -> Option<Self> {
if Self::is_in_subset(element) {
Some(unsafe { Self::from_superset_unchecked(element) })
} else {
None
}
}

/// Use with care! Same as `self.to_superset` but without any property checks. Always succeeds.
unsafe fn from_superset_unchecked(element: &T) -> Self;

/// Checks if `element` is actually part of the subset `Self` (and can be converted to it).
fn is_in_subset(element: &T) -> bool;
}

/// Nested sets and conversions between them. Useful to work with substructures. It is preferable
/// to implement the `SupersetOf` trait instead of `SubsetOf` whenever possible (because
/// `SupersetOf` is automatically implemented whenever `SubsetOf` is.
///
/// The notion of "nested sets" is very broad and applies to what the types are _supposed to
/// represent_, independently from their actual implementation details and limitations. For
/// example:
/// * f32 and f64 are both supposed to represent reals and are thus considered equal (even if in
/// practice f64 has more elements).
/// * u32 and i8 are respectively supposed to represent natural and relative numbers. Thus, i8 is
/// a superset of u32.
/// * A quaterion and a 3x3 orthogonal matrix with unit determinant are both sets of rotations.
/// They can thus be considered equal.
///
/// In other words, implementation details due to machine limitations are ignored (otherwise we
/// could not even, e.g., convert a u64 to an i64). If considering those limintations are
/// important, other crates allowing you to query the limitations of given types should be used.
pub trait SupersetOf<T>: Sized {
/// The inverse inclusion map: attempts to construct `self` from the equivalent element of its
/// superset.
///
/// Must return `None` if `element` has no equivalent in `Self`.
fn to_subset(&self) -> Option<T> {
if self.is_in_subset() {
Some(unsafe { self.to_subset_unchecked() })
} else {
None
}
}

/// Checks if `self` is actually part of its subset `T` (and can be converted to it).
fn is_in_subset(&self) -> bool;

/// Use with care! Same as `self.to_subset` but without any property checks. Always succeeds.
unsafe fn to_subset_unchecked(&self) -> T;

/// The inclusion map: converts `self` to the equivalent element of its superset.
fn from_subset(element: &T) -> Self;
}

impl<SS: SubsetOf<SP>, SP> SupersetOf<SS> for SP {
#[inline]
fn to_subset(&self) -> Option<SS> {
SS::from_superset(self)
}

#[inline]
fn is_in_subset(&self) -> bool {
SS::is_in_subset(self)
}

#[inline]
unsafe fn to_subset_unchecked(&self) -> SS {
SS::from_superset_unchecked(self)
}

#[inline]
fn from_subset(element: &SS) -> Self {
element.to_superset()
}
}

macro_rules! impl_subset(
(\$(\$subset: ty as \$( \$superset: ty),+ );* \$(;)*) => {
\$(\$(
impl SubsetOf<\$superset> for \$subset {
#[inline]
fn to_superset(&self) -> \$superset {
*self as \$superset
}

#[inline]
unsafe fn from_superset_unchecked(element: &\$superset) -> \$subset {
*element as \$subset
}

#[inline]
fn is_in_subset(_: &\$superset) -> bool {
true
}
}
)+)*
}
);

impl_subset!(
u8    as u8, u16, u32, u64, usize, i8, i16, i32, i64, isize, f32, f64;
u16   as u8, u16, u32, u64, usize, i8, i16, i32, i64, isize, f32, f64;
u32   as u8, u16, u32, u64, usize, i8, i16, i32, i64, isize, f32, f64;
u64   as u8, u16, u32, u64, usize, i8, i16, i32, i64, isize, f32, f64;
usize as u8, u16, u32, u64, usize, i8, i16, i32, i64, isize, f32, f64;

i8    as i8, i16, i32, i64, isize, f32, f64;
i16   as i8, i16, i32, i64, isize, f32, f64;
i32   as i8, i16, i32, i64, isize, f32, f64;
i64   as i8, i16, i32, i64, isize, f32, f64;
isize as i8, i16, i32, i64, isize, f32, f64;

f32 as f32, f64;
f64 as f32, f64;
);
//#[cfg(feature = "decimal")]
//impl_subset!(
//    u8 as d128;
//    u16 as d128;
//    u32 as d128;
//    u64 as d128;
//    usize as d128;
//
//    i8 as d128;
//    i16 as d128;
//    i32 as d128;
//    i64 as d128;
//    isize as d128;
//
//    f32 as d128;
//    f64 as d128;
//    d128 as d128;
//);

impl<N1, N2: SupersetOf<N1>> SubsetOf<Complex<N2>> for Complex<N1> {
#[inline]
fn to_superset(&self) -> Complex<N2> {
Complex {
re: N2::from_subset(&self.re),
im: N2::from_subset(&self.im),
}
}

#[inline]
unsafe fn from_superset_unchecked(element: &Complex<N2>) -> Complex<N1> {
Complex {
re: element.re.to_subset_unchecked(),
im: element.im.to_subset_unchecked(),
}
}

#[inline]
fn is_in_subset(c: &Complex<N2>) -> bool {
c.re.is_in_subset() && c.im.is_in_subset()
}
}

macro_rules! impl_scalar_subset_of_complex(
(\$(\$t: ident),*) => {\$(
impl<N2: Zero + SupersetOf<\$t>> SubsetOf<Complex<N2>> for \$t {
#[inline]
fn to_superset(&self) -> Complex<N2> {
Complex {
re: N2::from_subset(self),
im: N2::zero()
}
}

#[inline]
unsafe fn from_superset_unchecked(element: &Complex<N2>) -> \$t {
element.re.to_subset_unchecked()
}

#[inline]
fn is_in_subset(c: &Complex<N2>) -> bool {
c.re.is_in_subset() && c.im.is_zero()
}
}
)*}
);

impl_scalar_subset_of_complex!(u8, u16, u32, u64, usize, i8, i16, i32, i64, isize, f32, f64);
#[cfg(feature = "decimal")]
impl_scalar_subset_of_complex!(d128);
```