Crate serde_nothing
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This crate defines “nothing” in terms of serde data model
and allows checking values and create such values using only Serialize and Deserialize traits.
Motivation
This crate is designed to generalize serialization pattern where struct fields with None/empty/default values are skipped on serialization and constructed on deserialization when missing.
Usually this pattern is coded using #[serde(default, skip_serializing_if = "Option::is_none/Vec::is_empty/is_default")].
Where is_default is a function defined as
fn is_default<T: Default + PartialEq>(value: &T) -> bool {
*value == T::default()
}The pattern works very well for field with concrete types and generic wrappers like Option, Vec and similar.
But using #[serde(default)] on field with generic type T would require Default bound added to the Deserialize impl.
And #[serde(skip_serializing_if = "is_default")] would require T: Default + PartialEq bound added to the Serialize impl.
This crate allows to implement this pattern without additional bounds.
Even more, it allows specialize for types that can be skipped.
That is, if field has type T that does not even have a value that would be appropriate to skip,
the code will continue work correctly and would simply always serialize the field and require the data for deserialization.
Magic? No, science!
This crate provides stateless Nothing type which is a special kind of serde::Serializer or serde::Deserializer.
Nothing can be used to serialize and deserialize “nothing” values.
“Nothing” values are None, empty collections, units,
structs and tuples where all fields are “nothing”
Serializing a “non-nothing” value with Nothing always fails.
As deserializer Nothing would visit most appropriate Visitor method
with matching kind of nothingness, like None, empty slice/sequence/map,
single-variant enum with nothing in discriminant and nothing in payload,
0 numeric value etc.
User would most probably want to use a shortcut and utilize is_nothing function for serialization
and from_nothing function for deserialization.
Structs
Serializer to serialize values into and from nothing.
Error type for Nothing deserializer.
Error type for Nothing serializer.
Functions
Returns some “nothing” value of the type. Or none if failed to create one.
Returns true if the value matches definition of “nothing”.
Typically deserializing from Nothing would yield same value.