如何在go地图中存储类型以便以后进行初始化

Question

I'm trying to implement a factory function that will return an instance of one of many structs that fulfil the contract of an interface X.

m := make(map[string] ?)
func init () {
    m["a"] = ?
    m["b"] = ?
}

type X interface { 
    y()
}

type A struct {}
func (a * A) y () {}

type B struct {}
func (b * B) y () {}


function factory(name string) X {
    return &m[name]{}
}

The code above is just a simplified demonstration of what I'm trying to achieve - looking for pointers for whether this is possible, or if there is a different go idiom to solve this kind of requirement that I'm missing.

Answer 1

You can use map[string]X, with X the interface (which can reference a value or a pointer of any object respecting X contract)

or if there is a different go idiom to solve this kind of requirement that I'm missing?

You can also use reflection (as in "Instance new Type") to implement your factory.

reflect.New(yourtype).Elem().Interface()

You can see a factory example in "is there a way to create an instance of a struct from a string?".

---

The quicker approach for a factory method (returning a new instance each time) is using a switch (like in this example):

// Create a new Widget interface based on WidgetType and set WidgetInfo
func New(wt WidgetType, wi WidgetInfo) Widget_iface {
    switch wt {
    case Widget_A:
        return newWidgetA(wi)
    case Widget_B:
        return newWidgetB(wi)
    }
    return nil
}