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tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSubtyping.ts(9,7): error TS2415: Class 'Derived<U>' incorrectly extends base class 'Base<string>'.
Types of property 'x' are incompatible.
Type 'String' is not assignable to type 'string'.
'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
==== tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSubtyping.ts (1 errors) ====
// subtype checks use the apparent type of the target type
// S is a subtype of a type T, and T is a supertype of S, if one of the following is true, where S' denotes the apparent type (section 3.8.1) of S:
class Base<U extends String> {
x: U;
}
// is String (S) a subtype of U extends String (T)? Would only be true if we used the apparent type of U (T)
class Derived<U> extends Base<string> { // error
~~~~~~~
!!! error TS2415: Class 'Derived<U>' incorrectly extends base class 'Base<string>'.
!!! error TS2415: Types of property 'x' are incompatible.
!!! error TS2415: Type 'String' is not assignable to type 'string'.
!!! error TS2415: 'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
x: String;
}
class Base2 {
x: String;
static s: String;
}
// is U extends String (S) a subtype of String (T)? Apparent type of U is String so it succeeds
class Derived2<U extends String> extends Base2 { // error because of the prototype's not matching, not because of the instance side
x: U;
}
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