Wasm Differences

In the wasm crate we can't always go one to one with the rust crate. Here are some differences/extra types in the WASM create. AsRef From and Into are implemented to go between the rust and wasm crate types to help.

Heterogeneous Arrays

wasm_bindgen cannot expose doubly-nested types like Vec<Vec<T> which can be a limitation if T was a non-byte primitive. Any array of non-primitives such as [foo] will generate another type called FooList which supports all basic array operations. This lets us get around the wasm_bindgen limitation (without implementing cross-boundary traits which could be inefficient/tedious/complicated). This array wrapper implements len() -> self, get(usize) -> T and add(T).

Tables

Map literals also generate a type for them with len() -> usize and insert(K, V) -> Option<V>. The table type will have a MapKeyToValue name for whichever Key and Value types it's exposed as if it's anonymously inlined as a member, or will take on the identifier if it's a named one.

Enums

Both type/group choices generate rust-style enums. On the wasm side we can't do that so we directly wrap the rust type, and then provide a FooKind c-style enum for each rust enum Foo just for checking which variant it is.