Struct smart_config::de::Optional

pub struct Optional<De, const AND_THEN: bool = false>(pub De);

Deserializer decorator that wraps the output of the underlying decorator in Some and returns None if the input for the param is missing.

Encoding nulls

For env variables, specifying null values can be tricky since natively, all env variable values are strings. There are the following was to avoid this issue:

• JSON coercion can be used to pass unambiguous JSON values (incl. null).
• If the original deserializer doesn’t expect string values, an empty string or "null" will be coerced to a null.
• deserialize_if attribute can help filtering out empty strings etc. for types that do expect string values.

Transforms

The second generic param is the transform determining how the wrapped deserializer is delegated to. Regardless of the transform, missing and null values always result in None; any other value, will be passed to the wrapped deserializer.

• The default transform (AND_THEN == false) is similar to map. It requires the underlying deserializer to return a non-optional value.
• AND_THEN == true is similar to and_then. It expects the underlying deserializer to return an Option.

Tuple Fields

0: De

Implementations

impl<De> Optional<De>

pub const fn map(deserializer: De) -> Self

Wraps a deserializer returning a non-optional value, similarly to Option::map().

impl<De> Optional<De, true>

pub const fn and_then(deserializer: De) -> Self

Wraps a deserializer returning an optional value, similarly to Option::and_then().

Trait Implementations

impl<De: Debug, const AND_THEN: bool> Debug for Optional<De, AND_THEN>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T, De: DeserializeParam<T>> DeserializeParam<Option<T>> for Optional<De>

const EXPECTING: BasicTypes = De::EXPECTING

Describes which parameter this deserializer is expecting.

fn describe(&self, description: &mut TypeDescription)

Additional info about the deserialized type, e.g., extended description.

fn deserialize_param( &self, ctx: DeserializeContext<'_>, param: &'static ParamMetadata, ) -> Result<Option<T>, ErrorWithOrigin>

Performs deserialization given the context and param metadata.

fn serialize_param(&self, param: &Option<T>) -> Value

Serializes the provided parameter to the JSON model.

impl<T, De> DeserializeParam<Option<T>> for Optional<De, true>

where De: DeserializeParam<Option<T>>,

const EXPECTING: BasicTypes = De::EXPECTING

Describes which parameter this deserializer is expecting.

fn describe(&self, description: &mut TypeDescription)

Additional info about the deserialized type, e.g., extended description.

fn deserialize_param( &self, ctx: DeserializeContext<'_>, param: &'static ParamMetadata, ) -> Result<Option<T>, ErrorWithOrigin>

Performs deserialization given the context and param metadata.

fn serialize_param(&self, param: &Option<T>) -> Value

Serializes the provided parameter to the JSON model.