英文:
Can't access function when passing object and catching it in a interface{}
问题
这是我尝试做的事情：
package products
ProductManager struct {
products []*Product
index int64
}
func NewPM() *ProductManager {
return &ProductManager{}
}
func (p *ProductManager) List() []*Product {
return p.products
}
---
var productManager = products.NewPM()
func main() {
api := Api{}
api.Attach(productManager, "/products")
}
func (api Api) Attach(rm interface{}, route string) {
// 将典型的 REST 操作应用到 Mux。
// 例如：Product - 对应 /products
mux.Get(route, http.HandlerFunc(index(rm)))
}
func index(rm interface{}) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
// allRecords := rm.List() - 无法调用。找不到方法。
result := reflect.TypeOf(rm) // 可以工作，显示正确的类型。
method := result.Method(0).Name // 也可以工作！显示类型上的一个函数。
w.Write([]byte(fmt.Sprintf("%v", method)))
}
}
为什么我无法在productManager对象上调用List()函数？我可以看到类型的函数，甚至在index()处理程序中获取正确的类型名称。
英文:
Here's what I'm trying to do:
package products
ProductManager struct {
products []*Product
index int64
}
func NewPM() *ProductManager {
return &ProductManager{}
}
func (p *ProductManager) List() []*Product {
return p.products
}
---
var productManager = products.NewPM()
func main() {
api := Api{}
api.Attach(productManager, "/products")
}
func (api Api) Attach(rm interface{}, route string) {
// Apply typical REST actions to Mux.
// ie: Product - to /products
mux.Get(route, http.HandlerFunc(index(rm)))
}
func index(rm interface{}) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
// allRecords := rm.List() - DOESN'T WORK. No method found.
result := reflect.TypeOf(rm) // Works, shows me the correct type.
method := result.Method(0).Name // Works as well! Shows me a function on the type.
w.Write([]byte(fmt.Sprintf("%v", method)))
}
}
Any idea on why I can't call the List() function on my productManager object? I can see the Type's functions and even get the right Type name in the index() handler.
答案1
得分: 2
简单来说，rm是一个空接口变量，因此它没有任何方法，这正是interface{}的含义：没有方法。如果你知道rm的动态类型是*ProductManager，你可以进行类型断言（但这样你可以传递一个*ProductManager）。也许在长期运行中，你需要对rm进行类型切换。顺便说一句：几乎总是使用interface{}都是一个不好的主意。
英文:
Dead simple: rm is an empty interface variable, so it does not have any methods, that's exactly what interface{} means: No methods. If you know that rm's dynamic type is *ProductManager you can type assert it (but than you could pass a *ProductManager) Maybe you'll have to type switch on rm in the longer run. (BTW: using interface{} is almost always a bad idea.)
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