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Go Language Go Language Overview Custom Types Interfaces

Posted by danielkimeli
danielkimeli
1,196 Points

Another Go interface solution I can get past

In the clock and calendar packages, we've defined Clock and Calendar types, both of which have a Display method that you can call to print them. In the schedule package, define a Displayable interface that is satisfied by the Display methods on both the Clock and Calendar types. (Don't make any changes to the clock or calendar packages.) Then, still in the schedule package, define a Print function that takes a Displayable value and calls Display on it.

src/schedule/schedule.go 
package schedule


type Displayable interface {
  Display() int
}

func Print (display Displayable) int {
  d := display.Display()
   return d
}
src/clock/clock.go 
package clock

import "fmt"

type Clock struct {
  Hours int
  Minutes int
}

func (c Clock) Display() {
  fmt.Printf("%02d:%02d", c.Hours, c.Minutes)
}
src/calendar/calendar.go 
package calendar

import "fmt"

type Calendar struct {
  Year int
  Month int
  Day int
}

func (c Calendar) Display() {
  fmt.Printf("%04d-%02d-%02d", c.Year, c.Month, c.Day)
}

3 Answers

Gerald Wells
Gerald Wells
12,763 Points

A concrete type specifies exact representation of its values and exposes intrinsic opertations.
An interface on the other hand is an abstract type. It doesn't expose the representation or internal structure of its values or the set of basic operations they support; it reverals only some of their methods.
In saying this we can infer that the interface itself only needs to know what methods will be used not the context behind them. You can abstract that one more layer and write and interface for an interface(but I won't get into that).

package schedule

// DECLARE A Displayable INTERFACE HERE
type Displayable interface {
  Display()
 }

The function is calling d with a type of Displayable interface. 

// DECLARE A Print FUNCTION HERE
func Print( d Displayable) {
  d.Display()
 }
danielkimeli
danielkimeli
1,196 Points

Thanks this actually worked, I have know where i went wrong on from your explanation and >Steven Parker's above thanks again

Steven Parker
Steven Parker
230,069 Points
Steven Parker
Steven Parker
230,069 Points

In your interface, you define "Display()" as returning an "int". But if you look at the function implementations in the other files, you will see that neither one has any return value.

Then, your "Print" function is also defined to return an "int", and in the code it gets it from calling "Display()". But since that call does not actually return a value you won't be able to assign it to anything. And you probably don't need to make "Print" return anything, either.

danielkimeli
danielkimeli
1,196 Points

Thank you, your explanation was very clear, and with the help of the code below I managed it.

Steven Parker
Steven Parker
230,069 Points
Steven Parker
Steven Parker
230,069 Points

I intentionally did not provide code because I think most people have a better learning experience if they complete it themselves with a few hints.

danielkimeli
danielkimeli
1,196 Points
danielkimeli
danielkimeli
1,196 Points

I know, I applied it here https://teamtreehouse.com/community/i-cant-find-a-solution-to-struct-challenge