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June 19, 2022 03:53
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Omitting `symbol` and `number` from `keyof` on generic type using `Exclude`
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// Example showing usage of typescripts `Exclude` utility type. | |
// Typescript playground link: https://www.typescriptlang.org/play?#code/FAYw9gdgzgLgBAQwG4JAgJmKBJdcC8cAjAEwDMA3MKJLIgA70A2AplAMoCeAtgXF9wBGYJgAoARAkaso4gJTUAlhBgsATgDNULOADE1AV0UwAQgigBrFvADewOA7gBtKczYCAugC44EA0PV7RzA1BAgAczYfPwC1IId6FgQ1KGj-QUDHZ2RUDCxcb190wIBfag0DCBAYRUg4DUNjABUwAFFuMAArRVEGoxgAOQRuFh9YNWVwuTGYCYi4OyyoAHdjEAALOF7GweGWOQX4rLg0KB1xELDI2S8j48c1awM1CDhxQB4NwCl98TvHU-PEskbr97o8YM9Xh9AAr7P3uDnQLC0BiYMFucOOYIhbwAPJULBAwMsIAA+WGOMplYAVKo1Or0OYwfT9IYjbFNAA0cAA0nAWAAPVQQdBQOCtPkgJgGBHYqycMAaOAcuBQHjCJhwAA+RVixOJ22Zex8XM5gnMVlRiumytmk0OWVY8D6xnaXUUfCdMBaLu6+uMLP2Rwd9R2A38fFNlmsTg9-o8R0xLzgAAMACQ2D3exQlOBpmP+EpJ4CUoMR80+JnGMyR+CERaOFzSdw8QoAVnZR0uESixHbWUBKR8ZF79ZyaEwOHQhQALO3KQB6OeitRqEIi1Ywda3BeOACCanC-hYKjg8rgME4iTgAHJJI3ZFe4IoRQT4OYoIpwhAEIJWGewHB6GSPZVDUE8FXPS8b07a5xE1N5+3vYAFyQxdwGgEQWAAOiYMBwlEellEZEM9gkVwZHEE0zWsOQFBQpcVxSOB103OiHD3A8RmPU8IJ0K9KkUABHAwdBVIQRAfJ9fDAV8oHfT9v1-GB-0A0IRhAsCzwvXiLlCLtZDg8QEPEK9MJQui0KgDDsNw-CGQrXYRlEMim24Sjqxo6ht1aZdVyY4wWO3Nj90PLjwK069SDICTn2kxBZI-L8fx0JSAKAtT1A0njrx0q42FgrVDKSFJjLM7cLKsnC8IIlR7P9JyUDHfJ0Dc80PLogAFBlUlYt53ihOAyB+crWGsqq7OIxzCqBCi4FLaiFCAA | |
const avacadosId = 123; | |
const applesSym = Symbol("apples") | |
interface FruitBasket { | |
[applesSym]: number | |
oranges: number | |
pears: number | |
[avacadosId]: number | |
} | |
function fruitToEmoji(fruitName: string): string { | |
switch (fruitName) { | |
case "oranges": | |
return "🍊" | |
case "pears": | |
return "🍐" | |
default: | |
return "<unknown>" | |
} | |
} | |
function printFruitName<T, K extends Exclude<keyof T, symbol | number>>(fruitName: K, basket: T): string { | |
let fruitEmoji = fruitToEmoji(fruitName) | |
let fruitNum = basket[fruitName] | |
return `${fruitEmoji} ${fruitNum}` | |
} | |
let basket: FruitBasket = { | |
[applesSym]: 5, | |
oranges: 1, | |
pears: 3, | |
[avacadosId]: 4, | |
} | |
// Errors with: | |
// Argument of type '"apples"' is not assignable to parameter of type '"oranges" | "pears"' | |
// | |
// console.log(printFruitName("apples", basket)) | |
// Errors with: | |
// Argument of type 'unique symbol' is not assignable to parameter of type '"oranges" | "pears"'. | |
// | |
// console.log(printFruitName(applesSym, basket)) | |
// Errors with: | |
// Argument of type '123' is not assignable to parameter of type '"oranges" | "pears"' | |
// | |
// console.log(printFruitName(avacadosId, basket)) | |
// Prints: | |
// "🍐 3" | |
console.log(printFruitName("pears", basket)) |
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