tests/cases/compiler/assignToFn.ts(8,5): error TS2322: Type 'string' is not assignable to type '(n: number) => boolean'. ==== tests/cases/compiler/assignToFn.ts (1 errors) ==== module M { interface I { f(n:number):boolean; } var x:I={ f:function(n) { return true; } }; x.f="hello"; ~~~ !!! error TS2322: Type 'string' is not assignable to type '(n: number) => boolean'. }