René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Mapped conditional types","articleBody":"#12114 added mapped types, including recursive mapped types. [But as pointed out by @ahejlsberg](https://github.com/Microsoft/TypeScript/pull/12114#issuecomment-259776847)\r\n\u003e Note, however, that such types aren't particularly useful without some form of conditional type that makes it possible to limit the recursion to selected kinds of types.\r\n```ts\r\ntype primitive = string | number | boolean | undefined | null;\r\ntype DeepReadonly\u003cT\u003e = T extends primitive ? T : DeepReadonlyObject\u003cT\u003e;\r\ntype DeepReadonlyObject\u003cT\u003e = {\r\n    readonly [P in keyof T]: DeepReadonly\u003cT[P]\u003e;\r\n};\r\n```\r\nI couldn't find an existing issue with a feature request.\r\n\r\nConditional mapping would greatly improve the ergonomics of libraries like Immutable.js.\r\n","author":{"url":"https://github.com/matt-hensley","@type":"Person","name":"matt-hensley"},"datePublished":"2016-11-21T21:08:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":62},"url":"https://github.com/12424/TypeScript/issues/12424"}