Yeah, in your example the structure is sufficiently dissimilar to a string for TypeScript not to confuse them for each other. However, if you also have an identity provider returning UserInfo objects in the form of {'domain':'example.com', 'user':'john-doe'}, you might not like it that now any email address is a valid UserInfo object. On the type level in TS, you cannot tell those types apart. But I guess you figured that out already.