Within my TypeScript program, I have defined two base types (Player, State) and a few nested Record types that serve as mappings.
Using a typed function, an instance of one of these records is created based on an existing instance of the nested record.
type Player = "1" | "2";
type State = "A" | "B" | "C";
type StateMapping = Record<State, State>;
type PlayerStateMappings = Record<Player, StateMapping>
type PlayerStates = Record<Player, State>;
const playerStateMappings: PlayerStateMappings = {
"1": {
"A": "B",
"B": "C",
"C": "A"
},
"2": {
"C": "B",
"B": "A",
"A": "C"
},
}
function nextStates(currentState: State): PlayerStates {
var nextStates = {};
for(const player of Object.keys(playerStateMappings)){
nextStates[player] = playerStateMappings[player][currentState]
}
return nextStates;
}
console.log(nextStates("A"))
An issue arises with this code where a type error occurs at the return statement because the object was initially created without the required keys and added later:
TS2739: Type '{}' is missing the following properties from type 'PlayerStates': 1, 2I am seeking a solution to avoid this type error by meeting the following criteria:
- The typesystem must remain strict, ensuring the
nextStatesfunction returns a complete and validPlayerStatesobject. - The
nextStatesobject should be generated programmatically based on the keys of theplayerStatesMappingobject, eliminating the need to hardcode all players again.
Several potential solutions found on SO either compromise condition 1 or 2:
Approaches violating condition 1:
- Making the PlayerStates type partial:
type PlayerStates = Partial<Record<Player, State>>; - Enforcing type using the
askeyword:
; (from this question)var nextStates = {} as PlayerStates
Approaches violating condition 2:
- Setting default values for each Player in the object creation:
var nextStates = {"1": "A", "2": "B"}
Although the typing may seem excessive in this simplified example, it accurately reflects more complex projects where the mentioned requirements are crucial.
PS: With a background in Python, I am looking for a functionality similar to dict comprehension that would facilitate initializing a new dictionary based on iteration.