In TS <=3.3.3, the assignment in index.ts works fine. In TS 3.4.0-dev.20190216, it fails to compile with the following error output:
index.ts:6:5 - error TS2322: Type 'Maybe<Person>' is not assignable to type 'Maybe<Partial<Person>>'.
Type 'Just<Person>' is not assignable to type 'Maybe<Partial<Person>>'.
Type 'Just<Person>' is not assignable to type 'Just<Partial<Person>>'.
Types of property 'isJust' are incompatible.
Type '(this: Maybe<Person>) => this is Just<Person>' is not assignable to type '(this: Maybe<Partial<Person>>) => this is Just<Partial<Person>>'.
The 'this' types of each signature are incompatible.
Type 'Maybe<Partial<Person>>' is not assignable to type 'Maybe<Person>'.
Type 'Just<Partial<Person>>' is not assignable to type 'Maybe<Person>'.
Type 'Just<Partial<Person>>' is not assignable to type 'Just<Person>'.
Types of property 'value' are incompatible.
Type 'Partial<Person>' is not assignable to type 'Person'.
6 let wrapped: Maybe<Partial<Person>> = Maybe.of(me);
~~~~~~~
Possibly of interest: the direction that assignment is said not to satisfy the type requirements flips after the statement that The 'this' types of each signature are incompatible.: from the original Type 'Maybe<Person>' is not assignable to type 'Maybe<Partial<Person>>' to Type 'Maybe<Partial<Person>>' is not assignable to type 'Maybe<Person>'. This seems backwards.