tests/cases/compiler/incompatibleTypes.ts(5,7): error TS2420: Class 'C1' incorrectly implements interface 'IFoo1'. Types of property 'p1' are incompatible. Type '() => string' is not assignable to type '() => number'. Type 'string' is not assignable to type 'number'. tests/cases/compiler/incompatibleTypes.ts(15,7): error TS2420: Class 'C2' incorrectly implements interface 'IFoo2'. Types of property 'p1' are incompatible. Type '(n: number) => number' is not assignable to type '(s: string) => number'. Types of parameters 'n' and 's' are incompatible. Type 'number' is not assignable to type 'string'. tests/cases/compiler/incompatibleTypes.ts(25,7): error TS2420: Class 'C3' incorrectly implements interface 'IFoo3'. Types of property 'p1' are incompatible. Type 'number' is not assignable to type 'string'. tests/cases/compiler/incompatibleTypes.ts(33,7): error TS2420: Class 'C4' incorrectly implements interface 'IFoo4'. Types of property 'p1' are incompatible. Type '{ c: { b: string; }; d: string; }' is not assignable to type '{ a: { a: string; }; b: string; }'. Property 'a' is missing in type '{ c: { b: string; }; d: string; }'. tests/cases/compiler/incompatibleTypes.ts(42,5): error TS2345: Argument of type 'C1' is not assignable to parameter of type 'IFoo2'. Types of property 'p1' are incompatible. Type '() => string' is not assignable to type '(s: string) => number'. Type 'string' is not assignable to type 'number'. tests/cases/compiler/incompatibleTypes.ts(49,5): error TS2345: Argument of type '{ e: number; f: number; }' is not assignable to parameter of type '{ c: { b: string; }; d: string; }'. Property 'c' is missing in type '{ e: number; f: number; }'. tests/cases/compiler/incompatibleTypes.ts(66,5): error TS2322: Type '{ e: number; f: number; }' is not assignable to type '{ a: { a: string; }; b: string; }'. Property 'a' is missing in type '{ e: number; f: number; }'. tests/cases/compiler/incompatibleTypes.ts(72,5): error TS2322: Type 'number' is not assignable to type '() => string'. tests/cases/compiler/incompatibleTypes.ts(74,5): error TS2322: Type '(a: any) => number' is not assignable to type '() => any'. ==== tests/cases/compiler/incompatibleTypes.ts (9 errors) ==== interface IFoo1 { p1(): number; } class C1 implements IFoo1 { // incompatible on the return type ~~ !!! error TS2420: Class 'C1' incorrectly implements interface 'IFoo1'. !!! error TS2420: Types of property 'p1' are incompatible. !!! error TS2420: Type '() => string' is not assignable to type '() => number'. !!! error TS2420: Type 'string' is not assignable to type 'number'. public p1() { return "s"; } } interface IFoo2 { p1(s:string): number; } class C2 implements IFoo2 { // incompatible on the param type ~~ !!! error TS2420: Class 'C2' incorrectly implements interface 'IFoo2'. !!! error TS2420: Types of property 'p1' are incompatible. !!! error TS2420: Type '(n: number) => number' is not assignable to type '(s: string) => number'. !!! error TS2420: Types of parameters 'n' and 's' are incompatible. !!! error TS2420: Type 'number' is not assignable to type 'string'. public p1(n:number) { return 0; } } interface IFoo3 { p1: string; } class C3 implements IFoo3 { // incompatible on the property type ~~ !!! error TS2420: Class 'C3' incorrectly implements interface 'IFoo3'. !!! error TS2420: Types of property 'p1' are incompatible. !!! error TS2420: Type 'number' is not assignable to type 'string'. public p1: number; } interface IFoo4 { p1: { a: { a: string; }; b: string; }; } class C4 implements IFoo4 { // incompatible on the property type ~~ !!! error TS2420: Class 'C4' incorrectly implements interface 'IFoo4'. !!! error TS2420: Types of property 'p1' are incompatible. !!! error TS2420: Type '{ c: { b: string; }; d: string; }' is not assignable to type '{ a: { a: string; }; b: string; }'. !!! error TS2420: Property 'a' is missing in type '{ c: { b: string; }; d: string; }'. public p1: { c: { b: string; }; d: string; }; } function if1(i: IFoo1): void; function if1(i: IFoo2): void; function if1(a: any) { } var c1: C1; var c2: C2; if1(c1); ~~ !!! error TS2345: Argument of type 'C1' is not assignable to parameter of type 'IFoo2'. !!! error TS2345: Types of property 'p1' are incompatible. !!! error TS2345: Type '() => string' is not assignable to type '(s: string) => number'. !!! error TS2345: Type 'string' is not assignable to type 'number'. function of1(n: { a: { a: string; }; b: string; }): number; function of1(s: { c: { b: string; }; d: string; }): string; function of1(a: any) { return null; } of1({ e: 0, f: 0 }); ~~~~~~~~~~~~~~ !!! error TS2345: Argument of type '{ e: number; f: number; }' is not assignable to parameter of type '{ c: { b: string; }; d: string; }'. !!! error TS2345: Property 'c' is missing in type '{ e: number; f: number; }'. interface IMap { [key:string]:string; } function foo(fn:() => void) { } function bar() { var map:IMap; foo(() => { map = {}; }); } var o1: { a: { a: string; }; b: string; } = { e: 0, f: 0 }; ~~ !!! error TS2322: Type '{ e: number; f: number; }' is not assignable to type '{ a: { a: string; }; b: string; }'. !!! error TS2322: Property 'a' is missing in type '{ e: number; f: number; }'. var a1 = [{ e: 0, f: 0 }, { e: 0, f: 0 }, { e: 0, g: 0 }]; var i1c1: { (): string; } = 5; ~~~~ !!! error TS2322: Type 'number' is not assignable to type '() => string'. var fp1: () =>any = a => 0; ~~~ !!! error TS2322: Type '(a: any) => number' is not assignable to type '() => any'.