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lucas-jones/Typescript Union Handler

Created May 17, 2020 20:05
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Typescript Union Handler
enum Opcodes {
NAME_CHANGE = "nameChange",
POSITION = "position"
}
type NameChangePacket = {
opcode: Opcodes.NAME_CHANGE,
name: string
};
type PositionPacket = {
opcode: Opcodes.POSITION,
x: number,
y: number
};
type Packets = NameChangePacket | PositionPacket;
const packet: Packets = {
} as any;
type PacketsOfType<T extends Opcodes> = Extract<Packets, { opcode: T }>;
const on = <T extends Opcodes>(opcode: T, onPacket: (packet: PacketsOfType<T>) => void) => (packet: Packets) => {
if (packet.opcode === opcode) {
onPacket(packet as PacketsOfType<T>);
}
};
on(Opcodes.NAME_CHANGE, (packet) => {
console.log(packet.name)
})
on(Opcodes.POSITION, (packet) => {
console.log(packet.x)
})
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