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//! Module for [`SerializeAs`][] implementations //! //! The module contains the [`SerializeAs`][] trait and helper code. //! Additionally, it contains implementations of [`SerializeAs`][] for types defined in the Rust Standard Library or this crate. //! //! You can find more details on how to implement this trait for your types in the documentation of the [`SerializeAs`][] trait and details about the usage in the [user guide][]. //! //! [user guide]: crate::guide mod impls; use super::*; /// A **data structure** that can be serialized into any data format supported by Serde, analogue to [`Serialize`]. /// /// The trait is analogue to the [`serde::Serialize`][`Serialize`] trait, with the same meaning of input and output arguments. /// It can and should the implemented using the same code structure as the [`Serialize`] trait. /// As such, the same advice for [implementing `Serialize`][impl-serialize] applies here. /// /// # Differences to [`Serialize`] /// /// The trait is only required for container-like types or types implementing specific conversion functions. /// Container-like types are [`Vec`][], [`BTreeMap`][], but also [`Option`][] and [`Box`][]. /// Conversion types serialize into a different serde data type. /// For example, [`DisplayFromStr`] uses the [`Display`] trait to serialize a String and [`DurationSeconds`] converts a [`Duration`] into either String or integer values. /// /// This code shows how to implement [`Serialize`] for [`Box`]: /// /// ```rust,ignore /// impl<T> Serialize for Box<T> /// where /// T: Serialize, /// { /// #[inline] /// fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> /// where /// S: Serializer, /// { /// (**self).serialize(serializer) /// } /// } /// ``` /// /// and this code shows how to do the same using [`SerializeAs`][]: /// /// ```rust,ignore /// impl<T, U> SerializeAs<Box<T>> for Box<U> /// where /// U: SerializeAs<T>, /// { /// fn serialize_as<S>(source: &Box<T>, serializer: S) -> Result<S::Ok, S::Error> /// where /// S: Serializer, /// { /// SerializeAsWrap::<T, U>::new(source).serialize(serializer) /// } /// } /// ``` /// /// It uses two type parameters, `T` and `U` instead of only one and performs the serialization step using the `SerializeAsWrap` type. /// The `T` type is the on the Rust side before serialization, whereas the `U` type determines how the value will be serialized. /// These two changes are usually enough to make a container type implement [`SerializeAs`][]. /// /// [`BTreeMap`]: std::collections::BTreeMap /// [`Display`]: std::fmt::Display /// [`Duration`]: std::time::Duration /// [impl-serialize]: https://serde.rs/impl-serialize.html pub trait SerializeAs<T> { /// Serialize this value into the given Serde serializer. fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error> where S: Serializer; } /// Helper type to implement [`SerializeAs`] for container-like types. #[derive(Debug)] pub struct SerializeAsWrap<'a, T, U> { value: &'a T, marker: PhantomData<U>, } impl<'a, T, U> SerializeAsWrap<'a, T, U> { /// Create new instance with provided value. pub fn new(value: &'a T) -> Self { Self { value, marker: PhantomData, } } } impl<'a, T, U> Serialize for SerializeAsWrap<'a, T, U> where U: SerializeAs<T>, { fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where S: Serializer, { U::serialize_as(self.value, serializer) } } impl<'a, T, U> From<&'a T> for SerializeAsWrap<'a, T, U> where U: SerializeAs<T>, { fn from(value: &'a T) -> Self { Self::new(value) } }