Add example of type assertions

[adriancuadrado]

Resources:

• https://go.dev/ref/spec#Type_assertions
• https://go.dev/tour/methods/15

[eliben]

This could be useful if a good example can be worked out. There's some related code in the switch and json examples already, but maybe this would go to interfaces

[kevin-kho]

This could be useful if a good example can be worked out. There's some related code in the switch and json examples already, but maybe this would go to interfaces

I recommend this to go into interfaces. The perimeter of a circle is also called a circumference so a circum() method could be defined on the circle struct that does the same as perim(). Do type assertion against a shape to check if it's circle or rect before calling either perim() or circum()

Example below

// alias for perim()
func(c circle) circum() float64 {
    return c.perim()
}


shapeSlice := []geometry{rect{width: 5, length: 10}, circle{radius: 5}}

for _, shape := range shapeSlice {

    fmt.Println(shape.area())

    if r, ok := shape.(rect); ok {
       fmt.Println(r.perim())
    }

    if c, ok := shape.(circle); ok {
       fmt.Println(r.circum())
    }

}

Edit: made a PR. The example in PR is simpler than above stated example