Migrating from PromiseKit

Similarities

Below are some PromiseKit operations and their equivalents in Async+:

• firstly -> attempt
• then -> then (but it doesn't always need to return a value)
• map -> then with a non-async body returning a value
• compactMap -> use then returning a value, combined with a helper extension for optional called unwrapOrThrow. Use this on the optional value when you return to replicate the behavior of compactMap.
• recover -> recover
• get -> then that doesn't return anything
• tap -> tap (not implemented yet)
• ensure -> ensure
• done -> then without returning a value
• catch -> catch
• finally -> finally

Differences

Additionally, these operations offer functionality that is different from PromiseKit:

• .catch() with throwing body: this essentially just maps errors to one another while preventing further calls to then.
• .throws(): If the chain is able to be evaluated instantaneously, then this returns the value or throws.
• .async(): Can use on a guarantee (which is returned by a non-throwing recover).
• .asyncOptional(): For failable async chains: Async call that returns an optional value of the result.
• .asyncResult(): Async call that returns a Swift.Result<T, Error> (the Async+ framework defines its own result type).
• .asyncThrows(): Async call that returns the value or throws.