I try to create a function to create a piece of chess almost like the document.createElement:
class pawn extends piece {
}
class bishop extends piece {
}
class rook extends piece {
}
class king extends piece {
}
class queen extends piece {
}
class knigth extends piece {
}
export interface pieces {
"pawn": pawn
"bishop": bishop
"rook": rook
"king": king
"queen": queen
"knigth": knigth
}
export function createPiece<K extends keyof pieces>(pieceName: K, options?: pieceInit): pieces[K]{
/// ???
}
But I don't know what I need to return in my createPiece function... I try
export function createPiece<K extends keyof pieces>(pieceName: K, options?: pieceInit): pieces[K]{
return pieces[pieceName]
}
But I got the following error : 'pieces' only refers to a type, but is being used as a value here
My goal is :
const piece1:pawn = createPiece("pawn");
const piece2:queen = createPiece("queen");
.
.
.
You defined pieces as an interface. You can only access information about interfaces during compile-time and not during runtime. That's why the line return pieces[pieceName] fails to compile.
You should instead define pieces as an object.
export const pieces = {
"pawn": pawn,
"bishop": bishop,
"rook": rook,
"king": king,
"queen": queen,
"knigth": knigth
}
We can use this object to look up the keys during runtime and we can also extract the type information of pieces for use during compile-time.
export function createPiece<
K extends keyof typeof pieces
>(pieceName: K): typeof pieces[K] {
return pieces[pieceName]
}
So instead of using pieces directly in the generic type, you can use typeof pieces to get the type of the pieces object.
You can if you define the interface as a const. Fully typed it would look like so:
type PiecesKey = keyof Pieces;
type Piece<T extends PiecesKey> = Pieces[T];
type Pieces = {
pawn: pawn;
bishop: bishop;
rook: rook;
king: king;
queen: queen;
knigth: knigth;
};
const pieces = {
pawn: pawn,
bishop: bishop,
rook: rook,
king: king,
queen: queen,
knigth: knigth,
};
type pieceInit = {};
export function createPiece<K extends PiecesKey>(
pieceName: K,
options?: pieceInit,
): Piece<K> {
return new pieces[pieceName]();
}
IN you function, you are returning return pieces pieces is a type. You cannot use a type like you would use a value. What are you trying to do more specifically? I will give you a hand :)