der 0.8.0

Pure Rust embedded-friendly implementation of the Distinguished Encoding Rules (DER) for Abstract Syntax Notation One (ASN.1) as described in ITU X.690 with full support for heapless `no_std`/`no_alloc` targets
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//! A module for working with referenced data.

/// A trait for borrowing data from an owned struct
///
/// This converts an object owning the data to one that will borrowing the content.
/// The newly created object lifetime will be tied to the object owning the data.
///
/// This is similar to [`alloc::borrow::Borrow`] or [`core::convert::AsRef`] but this returns
/// an owned structure that references directly the backing slices instead of borrowing
/// the whole structure.
pub trait OwnedToRef {
    /// The resulting type referencing back to Self
    type Borrowed<'a>
    where
        Self: 'a;

    /// Creates a new object referencing back to the self for storage
    fn owned_to_ref(&self) -> Self::Borrowed<'_>;
}

/// A trait for cloning a referenced structure and getting owned objects
///
/// This is the pendant to [`OwnedToRef`].
///
/// This converts an object borrowing data to one that will copy the data over and
/// own the content.
pub trait RefToOwned<'a> {
    /// The resulting type after obtaining ownership.
    type Owned: OwnedToRef<Borrowed<'a> = Self>
    where
        Self: 'a;

    /// Creates a new object taking ownership of the data
    fn ref_to_owned(&self) -> Self::Owned;
}

impl<T> OwnedToRef for Option<T>
where
    T: OwnedToRef,
{
    type Borrowed<'a>
        = Option<T::Borrowed<'a>>
    where
        T: 'a;

    #[allow(clippy::redundant_closure_for_method_calls, reason = "MSRV")]
    fn owned_to_ref(&self) -> Self::Borrowed<'_> {
        self.as_ref().map(|o| o.owned_to_ref())
    }
}

impl<'a, T> RefToOwned<'a> for Option<T>
where
    T: RefToOwned<'a> + 'a,
    T::Owned: OwnedToRef,
{
    type Owned = Option<T::Owned>;

    #[allow(clippy::redundant_closure_for_method_calls, reason = "MSRV")]
    fn ref_to_owned(&self) -> Self::Owned {
        self.as_ref().map(|o| o.ref_to_owned())
    }
}

#[cfg(feature = "alloc")]
mod allocating {
    use super::{OwnedToRef, RefToOwned};
    use alloc::boxed::Box;

    impl<'a> RefToOwned<'a> for &'a [u8] {
        type Owned = Box<[u8]>;

        fn ref_to_owned(&self) -> Self::Owned {
            Box::from(*self)
        }
    }

    impl OwnedToRef for Box<[u8]> {
        type Borrowed<'a> = &'a [u8];

        fn owned_to_ref(&self) -> Self::Borrowed<'_> {
            self.as_ref()
        }
    }
}