1. scale-info
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flowchart RL SI[[scale-info]] SIT1(Registry) SIT2(TypeInfo) SIT1-- struct -->SI SIT2-- trait -->SI
The scale-info Rust crate provides the essential tooling to handle type metadata in a compact, efficient manner compatible with the SCALE encoding. Its primary features include the Registry struct and the TypeInfo trait.
The Registry serves as a database that associates each type with its corresponding metadata, providing a convenient and efficient means to access necessary type data.
The TypeInfo trait, on the other hand, enables users to generate type information for any Rust type that implements this trait, which in turn can be registered in the Registry.
These features of scale-info provide the underpinning for flexible encoding and decoding, by allowing types to describe themselves in a way that can be exploited by encoding and decoding tools such as the scale-decode crate.
2. scale-decode
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flowchart TD SD[[scale-decode]] SDT1(Visitor) SDT1-- trait -->SD SDT4("decode_with_visitor (bytes, typeid, registry, visitor)")-- function -->SD SDT4-->Decode("SCALE bytes decoded into custom data structure")
The scale-decode crate facilitates the decoding of SCALE-encoded bytes into custom data structures by using type information from a scale-info registry. By implementing the Visitor trait and utilizing the decode_with_visitor function, developers can map decoded values to their chosen types with enhanced flexibility.
3. scale-value
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flowchart TD SD[[scale-value]] SDT1(Value) SDT1-- struct -->SD
This crate provides a Value type, which is a runtime representation that is compatible with type descriptions from scale-info. It somewhat analogous to a serde_json::Value, which is a runtime representation of JSON values, but with a focus on SCALE encoded values instead of JSON encoded values. Unlike JSON however, SCALE encoding is not self describing, and so we need additional type information to tell us how to encode and decode values. It is expected that this crate will commonly be used in conjunction with the scale-info and frame-metadata crates.
4. frame-metadata
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While not directly a part of SCALE, the frame-metadata crate utilizes a Registry from the scale-info crate. The frame-metadata crate provides a struct that encapsulates metadata about a Substrate runtime. A notable aspect of this struct is a type registry, which is a collection of all types utilized in the metadata of the runtime. In addition, the struct comprises comprehensive data on the runtime’s pallets, extrinsics, Runtime API, outer enums, and even accommodates custom metadata. The collective use of these elements allows developers to effectively navigate and adapt to the intricacies of a specific Substrate-based blockchain runtime.