Go 函数类型作为接口(interface)值

Question

我一直在阅读 function types as interface values在 go 中，我遇到了一个我无法弄清楚的例子。在这里:

type binFunc func(int, int) int

func add(x, y int) int { return x + y }

func (f binFunc) Error() string { return "binFunc error" }

func main() {
    var err error
    err = binFunc(add)
    fmt.Println(err)
}

您可以在 Go Playground 上找到它 here .

我知道您可以将方法分配给函数类型，但我不明白 Error() 是如何被调用的。

Answer 1

fmt 包的文档是这样说的:

Except when printed using the verbs %T and %p, special formatting considerations apply for operands that implement certain interfaces. In order of application:

...

If the format (which is implicitly %v for Println etc.) is valid for a string (%s %q %v %x %X), the following two rules apply:

4. If an operand implements the error interface, the Error method will be invoked to convert the object to a string, which will then be formatted as required by the verb (if any).
5. If an operand implements method String() string, that method will be invoked to convert the object to a string, which will then be formatted as required by the verb (if any).

换句话说，fmt.Println 将尝试打印接口(interface)的字符串表示形式。由于错误接口(interface)由binFunc满足，它调用binFunc的Error方法。