tests/cases/compiler/widenToAny1.ts(5,5): error TS2322: Type 'string' is not assignable to type 'number'. ==== tests/cases/compiler/widenToAny1.ts (1 errors) ==== function foo1(f1: { x: T; y: T }): T { return undefined; } var z1: number = foo1({ x: undefined, y: "def" }); // Best common type is any ~~ !!! error TS2322: Type 'string' is not assignable to type 'number'.