JuniorTheoryCommon

What happens when this program is built and run?

package main

import "fmt"

type Shape interface{ Area() float64 }
type Square struct{ Side int }

func (s Square) Area() int { return s.Side * s.Side }
func main() {
    var sh Shape = Square{Side: 2}
    fmt.Println(sh.Area())
}

It does not compile

Expecting 4: a type implements an interface only when each method has the same parameters and results, and this Area returns int, not float64.
Expecting a panic at run time: the compiler checks the methods when Square{Side: 2} is assigned to a Shape variable, so the program never runs.

How would you change Square so that the program compiles and prints 4?
Why does Go check interface satisfaction at compile time rather than at the call?

Back to questions Open topic in roadmap →Answer it yourself — Quiz

Back to questions

JuniorTheoryCommon

What happens when this program is built and run?

package main

import "fmt"

type Shape interface{ Area() float64 }
type Square struct{ Side int }

func (s Square) Area() int { return s.Side * s.Side }
func main() {
    var sh Shape = Square{Side: 2}
    fmt.Println(sh.Area())
}

It does not compile

Expecting 4: a type implements an interface only when each method has the same parameters and results, and this Area returns int, not float64.
Expecting a panic at run time: the compiler checks the methods when Square{Side: 2} is assigned to a Shape variable, so the program never runs.

How would you change Square so that the program compiles and prints 4?
Why does Go check interface satisfaction at compile time rather than at the call?

Back to questions Open topic in roadmap →Answer it yourself — Quiz