Function parameter object literal constraint

Hi, can anyone please explain why TypeScript gives error for `a2` but not for `a1`? ``` function A(a: { a: string; b: boolean }) { return a } const a = { a: '', b: true, c: 'string' } const a1 = A(a) const a2 = A({ a: '', b: true, c: 'string' }) ```