覆盖接口指针值

Question

I made an interface meant to do basic math with struct values. The interface's math functions always update the values of the struct's pointer.

My problem is that at some point, I want to overwrite the value to the initial value but I only have the interface to work with. Because it is a pointer interface (not 100% sure if this is what people call it), I am unable to "clone" the initial value of the struct in order to overwrite later.

Please also note I'm trying my best to avoid reflection.

Here is my code. Will probably make a lot more sense than me trying to explain it:

package main

import (
    "fmt"
)

type mather interface {
    add(mather) mather
    sub(mather) mather
}

type float struct {
    value float64
}

func (f *float) add(m mather) mather {
    f.value += m.(*float).value
    return f
}

func (f *float) sub(m mather) mather {
    f.value -= m.(*float).value
    return f
}

func (f *float) get() interface{} {
    return *f
}

func main() {
    var a, b, c mather

    a = &float{2} // this could be any time. approximitly 10 possible types
    b = &float{7} // this could be any time. approximitly 10 possible types

    // float can't be used again below, only mather

    c = a

    fmt.Println(a)
    fmt.Println(b)
    fmt.Println()

    // a's math
    doMath(a)

    // now math is done, we need to reset the value from before the math was done
    // set *a equal to *c. (a == &float{2})
    resetMath(a, c)

    // b's math
    doMath(b)

    // now math is done, we need to reset the value from before the math was done
    // set *b equal to *c. (b == &float{7})
    resetMath(b, c)

    fmt.Println(a)
    fmt.Println(b)

}

func doMath(m mather) {
    m.add(&float{3})
}

func resetMath(m mather, r mather) {
    m = r
}

https://play.golang.org/p/3Szk8uQGy5

Answer 1

You need to define clone and set method in mather interface, i.e.:

type mather interface {
    add(mather) mather
    sub(mather) mather
    get() interface{}
    clone() mather
    set(v mather)
}

The implementation of get, set and clone in float type looks like:

func (f *float) get() interface{} {
    return f.value
}

func (f *float) clone() mather {
    return &float{f.value}
}

func (f *float) set(v mather) {
    switch v := v.(type) {
    case *float:
        f.value = v.value
    //handle other possible types...
    default:
        //handle unknown types
    }
}

See working example in Playground. The only complicated parts is set in which you should determined the underlying type. Here you can use type switch to get underlying type, then assign it to float. Similar codes need to be added in the other underlying types (you mention that there are 10 possible types).