How to define an interface with properties?

php editor Yuzai will introduce to you how to define an interface with attributes. In PHP, an interface is a convention that defines the methods a class should implement. However, sometimes we also need to define properties in the interface. To define an interface with properties, we can use constants to simulate properties and assign values ​​in the class that implements the interface. In this way, we can define and use properties in the interface. Next, let's take a look at the specific implementation method.

Question content

I have a question: Is it possible to set an interface for a linear space?

Let me remind you that in linear space l, there are operations of adding elements and multiplying elements by numbers. In addition, two properties are also satisfied:

1) a b in

l

2)l in ak, where k - scalar

I present the interface for linear space in the following form:

type Point interface {
}

type LinSpace interface {
    Sum(x, y Point)
    Prod(x Point, k float64)
}

How to consider the above two properties in the interface definition?

Solution

Interfaces can only contain methods.

You can do this:

// effective go says: interface names should contain prefix -er 
    type linspacer interface {
        sum() float64
        prod(k float64) float64
    }
    
    // struct that implements interface
    type linspaceimpl struct {
        a float64
        b float64
    }
    
    // implementation of sum() method
    // also, you don't need to pass a and b vars
    // because they're already exist in linspaceimpl
    func (l *linspaceimpl) sum() float64 {
        return l.a + l.b
    }
    
    // implementation of prod() method
    // unlike the sum() method, here we need extra param - k
    // so it has to be passed, or you can add it to
    // linspaceimpl as another fields but it doesn't
    // make any sense though
    func (l *linspaceimpl) prod(k float64) float64 {
        return l.a * k
    }
    
    // unnecessary "constructor" to optimize your main function
    // and clarify code
    func newlinspace(a, b float64) linspacer {
    // since linspaceimpl correctly implements linspacer interface
    // you can return instance of linspaceimpl as linspacer
        return &linspaceimpl{
            a: a,
            b: b,
        }
    }

You can then do this in your main (or other) function:

// Use any float values
    ls := NewLinSpace(11.2, 24.7)
    
    fmt.Println(ls.Sum())      // 35.9
    fmt.Println(ls.Prod(30.2)) // 338.23999999999995

This is how "oop" works in go.

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