René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Mapped type optional -\u003e required property issue","articleBody":"**TypeScript Version:**  2.1.4\r\n\r\n**Code**\r\nhttps://github.com/JakeGinnivan/TypeScriptMappedTypeIssue\r\n\r\n**Expected behavior:**\r\nThe mapped type\r\n\r\n``` ts\r\nexport type PropDescriptions\u003cT\u003e = {\r\n    [P in keyof T]: string\r\n}\r\n```\r\n\r\nIs marking all the properties as required, I would expect this to fail:\r\n\r\n```\r\ninterface ThingProps {\r\n    prop1: string\r\n    prop2?: string\r\n}\r\n\r\nconst expected: PropDescriptions\u003cThingProps\u003e = {\r\n    prop1: 'Ok'\r\n}\r\n```\r\n\r\nwith `Property 'prop2' is missing in type {...}`\r\n\r\n**Actual behavior:**\r\nNo compilation error","author":{"url":"https://github.com/JakeGinnivan","@type":"Person","name":"JakeGinnivan"},"datePublished":"2016-12-30T07:41:14.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/13224/TypeScript/issues/13224"}