MetaSupplier

public protocol MetaSupplier

The core interface to specify MetaEncoder’s encoding. Implement this protocol to set encoding “primities” (these are usually the types you can represent directly in your serialization format) and container implementations.

containers

  • keyedContainerMeta() Default implementation

    Returns an empty EncodingKeyedContainerMeta.

    This method lets you use a custom container type (e.g. NSDictionary), if required. However this method has a default implementation returning a new Dictionary every time it is called.

    Attention

    You should implement this method or keep the default implementation of it, even if you do not support keyed containers in you framework, because the documentation of Encodable specifies an empty keyed container as substitute if a value did not encode anything. Do not use precondition or assert in this method for that reason. Also keyed containers are an important part of many encode(to:) implementations (especially the default generated ones). Therefor it could make sence to implement some transition from keyed containers to other containers you provide. A custom implementation of EncodingKeyedContainerMeta is the right place for this.

    Default Implementation

    Declaration

    Swift

    func keyedContainerMeta() -> EncodingKeyedContainerMeta

    Return Value

    A new, empty EncodingKeyedMetaContainer.

  • unkeyedContainerMeta() Default implementation

    Returns an empty EncodingUnkeyedMetaContainer.

    This method lets you use a custom container type (e.g. NSArray), if required. However this method has a default implementation returning a new Array every time it is called.

    Default Implementation

    Declaration

    Swift

    func unkeyedContainerMeta() -> EncodingUnkeyedContainerMeta

    Return Value

    A new, empty EncodingUnkeyedMetaContainer.

wrapper

  • Creates, sets and returns a Meta for the given value, or returns nil if the value is not supported, respectively can not be represented in your underlying format.

    This method will be asked to return a Meta for an instance of the type NilMarker from MetaSerialization if encoding a nil value is requested. Return nil if you don’t support nil values. If you support nil values, you are invited to use NilMarker itself as Meta, but you may of course use any meta implementation here.

    You may not call Encodables encode(to:) in this method directly, neighter one of the container methods. Calling these methods will conflict with the encoding of value, since you can not access the metas you created with those calls. Call encoder.encode instead and nest your container requests inside a utility type if necessary.

    This method is called very frequently.

    Declaration

    Swift

    func wrap<T>(_ value: T, for encoder: MetaEncoder) throws -> Meta? where T : Encodable

    Parameters

    value

    The value for which a wrapping meta should be returned.
    encoder

    The encoder that requests the wrap. You should use this encoder if you need to encode values yourself inside wrap or to get the current coding path (this an array of coding keys visited up to value in the order they were visited taken up to value). The coding path is ment to be used in errors you may throw (e.g. EncodingError).

    Return Value

    nil or a Meta which wrappes value.