类型开关的俱乐部值
以下代码工作正常
var requestMap map[string]interface{}
for _, value := range requestMap {
switch v := value.(type) {
case []interface{}:
if len(v) == 0 {
// if is empty then no need to throw NA
return http.StatusOK, nil
}
case string:
if len(v) == 0 {
// if is empty then no need to throw NA
return http.StatusOK, nil
}
}
}
，但是以下代码给出了len function的无效参数，我读过这个问题
var requestMap map[string]interface{}
for _, value := range requestMap {
switch v := value.(type) {
case []interface{}, string:
if len(v) == 0 {
// if is empty then no need to throw NA
return http.StatusOK, nil
}
}
}
此情况语句难道不够识别[]接口{} 或string作为值类型？ 为什么仍将接口{}作为len（）的参数
Following code is working fine
var requestMap map[string]interface{}
for _, value := range requestMap {
switch v := value.(type) {
case []interface{}:
if len(v) == 0 {
// if is empty then no need to throw NA
return http.StatusOK, nil
}
case string:
if len(v) == 0 {
// if is empty then no need to throw NA
return http.StatusOK, nil
}
}
}
But following code is giving invalid argument for len function, I have read this question
var requestMap map[string]interface{}
for _, value := range requestMap {
switch v := value.(type) {
case []interface{}, string:
if len(v) == 0 {
// if is empty then no need to throw NA
return http.StatusOK, nil
}
}
}
Isn't this case statement enough to identify []interface{} or string as value type ?
Why is it still considering interface{} as parameter of len()
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如果您在类型开关的
案例中列出了多种类型，则switch> switch变量的静态类型将是原始变量的类型。 spec：switch语句：因此，如果开关表达式为
v：= value。（type），在匹配案例中v（列表多种类型）将是value的类型，在您的情况下，它将是接口{}。 andininlen（）函数不允许通过值传递值类型接口{}。If you list multiple types in a
caseof a type switch, the static type of theswitchvariable will be of the type of the original variable. Spec: Switch statements:So if the switch expression is
v := value.(type), the ofvin the matching case (listing multiple types) will be the type ofvalue, in your case it will beinterface{}. And the builtinlen()function does not allow to pass values of typeinterface{}.这是因为在类型开关的情况下，应将
v转换为接口（[]接口）和String在同时。编译器无法决定要使用哪个，因此它将值还原为接口{}，因为它可以是任何东西。This is because in the case of the type switch, the
vshould be converted to a slice of interface ([]interface) and to astringat the same time. The compiler can't decide which to use, so it revert back the value tointerface{}, since it can be anything.