无法调用"+ ="参数类型为(Int，@value Int)的参数列表

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我有一个类Transaction，其类型为Int的可变金额. 我想从另一个有array of Transactions的类中访问它，并对它们的全部金额求和.

I have a class Transaction which has a var amount of type Int. I want to access it from another class, where I have an array of Transactions and sum all of their amounts.

所以我有这段代码

func computeTotal()-> Int{ let total = 0 for transaction in transactions{ //get the amounts of each and sum all of them up total += transaction.amount } return total }

但这给我一个错误

无法使用类型为(Int，@value Int)的参数列表调用"+ ="

是什么原因引起的?我知道在Swift中，两个操作数必须是同一类型，但是在我的代码中它们都是Int类型.

What can cause that? I know that in Swift both operands must be the same type, but they are both of type Int in my code.

推荐答案

let创建不可变的值.您需要使用var，例如:

let creates an immutable value. You need to use var, like:

func computeTotal()-> Int{ var total = 0 for transaction in transactions{ //get the amounts of each and sum all of them up total += transaction.amount } return total }