- if let operand = operandEvaluation.result { return (operation(operand), operandEvaluation.result) }
出错原因:initializer for conditional binding must have optional type ,not "Double"
-
return (nil, ops)
出错原因:nil is incompatible with reture type "Double"
return evaluate()
出错原因:unexpected non-void return value in void function
在Xcode6编译可以成功,但是Xcode7.1出错了,请问应该怎么改动才能正确