Question

运行以下内容时出现错误not enough arguments in call to method expression AccountService.Open。在此处运行：https://play.golang.org/p/Z9y-QIcwNy

type AccountService interface {
    Open(no string, name string, openingDate time.Time) AccountService
}

type Account struct {
    Num      string
    Name     string
    OpenDate time.Time
    Balance  float64
}

type SavingsAccount struct {
    InterestRate float32
    Account
}

type CheckingAccount struct {
    TransactionFee float32
    Account
}

func (a SavingsAccount) Open(no string, name string, openingDate time.Time) AccountService {
    return SavingsAccount{
        Account: Account{Num: no,
            Name:     name,
            OpenDate: openingDate,
        },
        InterestRate: 0.9,
    }
}
func (a CheckingAccount) Open(no string, name string, openingDate time.Time) AccountService {
    return CheckingAccount{
        Account: Account{Num: no,
            Name:     name,
            OpenDate: openingDate,
        },
        TransactionFee: 0.15,
    }
}

func main() {
    aliceAcct := AccountService.Open("12345", "Alice", time.Date(1999, time.January, 03, 0, 0, 0, 0, time.UTC))

    fmt.Println("Alice's account =", aliceAcct)
}

Answer 1

method expression AccountService.Open的结果是一个类型为func(AccountService, string, string, time.Time) AccountService的函数。代码缺少第一个参数。你可以这样称呼它：

aliceAcct := AccountService.Open(CheckingAccount{}, "12345", "Alice", time.Date(1999, time.January, 03, 0, 0, 0, 0, time.UTC))

playground example

如果您没有有意义的值用作接收器，请改用函数：

func OpenCheckingAccount(no string, name string, openingDate time.Time) AccountService {
    ...
}

如果您需要抽象帐户创建，请将服务定义为函数：

 type AccountService func(no string, name string, openingDate time.Time) AccountType
 func OpenSavings(no string, name string, openingDate time.Time) AccountType { ... }
 func OpenChecking(no string, name string, openingDate time.Time) AccountType { ... }

OpenSavings和OpenChecking函数可用作AccountService。

您需要为服务和帐户使用不同的类型。在这里，我使用AccountService和AccountType。 AccountType不是一个很好的名称，但已经使用了Account。 AccountType可能定义如下：

type AccountType interface {
   func Deposit(int)
   func Withdraw(int)
}

Answer 2

试试这个

acct := SavingsAccount{}
aliceAcct:= acct.Open("12345", "Alice", time.Date(1999, time.January, 03, 0, 0, 0, 0, time.UTC))
fmt.Println("Alice's account =", aliceAcct)

您需要创建一个正确实现AccountService接口的结构实例

- 编辑工作示例：play.golang.org

Answer 3

大多数Go包都会执行以下两项操作之一：

有一个包级别函数，例如OpenSavingsAccount，它返回一个打开的，初始化的SavingsAccount。
在名为DefaultSavingsAccount的包中有一个默认变量，并在包级别复制SavingsAccount方法，它们在DefaultSavingsAccount上运行。这是很多功能重复，但所有逻辑都保留在方法中。如果DefaultSavingsAccount不是const并且是接口类型，则可以用其他实现替换它。

如何在结构类型上调用Go方法？

3 个答案: