Interface satisfaction in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an interface named Speaker.

Go

type Speaker interface {
	[1]()
}

Drag options to blanks, or click blank then click option'

AListen

BSpeak

CTalk

DRun

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name not related to speaking, like 'Run'.

Forgetting the parentheses after the method name.

The interface Speaker requires a method named Speak with no parameters.

2fill in blank

medium

Complete the code to make type Dog satisfy the Speaker interface by implementing Speak method.

Go

package main

import "fmt"

type Dog struct {}

func (d Dog) [1]() {
	fmt.Println("Woof!")
}

Drag options to blanks, or click blank then click option'

ASpeak

BTalk

CRun

DListen

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name like 'Talk' or 'Run'.

Missing the method receiver in the function.

The method Speak is required to satisfy the Speaker interface.

3fill in blank

hard

Fix the error in the code to make type Cat satisfy the Speaker interface.

Go

package main

import "fmt"

type Cat struct {}

func (c Cat) [1]() {
	fmt.Println("Meow!")
}

Drag options to blanks, or click blank then click option'

ASpeak

BListen

CRun

DTalk

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name.

Changing the method signature (parameters or return type).

The method Speak must have the same signature as in the interface. Here it returns nothing, which is acceptable if the interface method has no return.

4fill in blank

hard

Fill both blanks to declare an interface and a type that satisfies it.

Go

type [1] interface {
	[2]()
}

type Bird struct {}

func (b Bird) [2]() {
	fmt.Println("Tweet!")
}

Drag options to blanks, or click blank then click option'

ASinger

BSpeak

CTalk

DRunner

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names in interface and type.

Naming interface with a verb instead of a noun.

The interface is named Singer and requires a method Speak. The type Bird implements Speak to satisfy the interface.

5fill in blank

hard

Fill all three blanks to create a function that accepts any Speaker and calls its Speak method.

Go

func [1](s [2]) {
	s.[3]()
}

Drag options to blanks, or click blank then click option'

AMakeSound

BSpeaker

CSpeak

DAnimal

Attempts:

3 left

💡 Hint

Common Mistakes

Using a concrete type instead of the interface as parameter.

Calling a method name not defined in the interface.

The function MakeSound takes a parameter of type Speaker interface and calls its Speak method.

Practice

1. Which statement best describes how a type satisfies an interface in Go?

easy

A. A type satisfies an interface by implementing all the methods declared in the interface.

B. A type satisfies an interface only if it explicitly declares it implements the interface.

C. A type satisfies an interface by embedding the interface in its struct definition.

D. A type satisfies an interface by having the same name as the interface.

Solution

1. Step 1: Understand interface satisfaction in Go

   In Go, a type satisfies an interface if it implements all the methods declared in that interface.

2. Step 2: Check explicit declaration requirement

   Go does not require explicit declaration; satisfaction is implicit by method implementation.

3. Final Answer:

   A type satisfies an interface by implementing all the methods declared in the interface. -> Option A

4. Quick Check:

   Interface satisfaction = implicit method implementation [OK]

Hint: Remember: Implement all methods, no explicit declaration needed [OK]

Common Mistakes:

• Thinking explicit declaration is required
• Confusing embedding with satisfaction
• Matching names instead of methods

2. Which of the following Go code snippets correctly shows a type satisfying an interface Speaker with method Speak()?

easy

A. type Speaker interface { Speak() string }
type Dog struct {}
func (d Dog) speak() string { return "Woof" }

B. type Speaker interface { Speak() string }
type Dog struct {}
func (d Dog) Speak() string { return "Woof" }

C. type Speaker interface { Speak() string }
type Dog struct {}
func Speak(d Dog) string { return "Woof" }

D. type Speaker interface { Speak() string }
type Dog struct {}
func (d *Dog) Speak() int { return 1 }

Solution

1. Step 1: Check method signature and receiver

   type Speaker interface { Speak() string } type Dog struct {} func (d Dog) Speak() string { return "Woof" } defines Speak() with correct receiver (d Dog) and return type string.

2. Step 2: Verify method name and return type match interface

   type Speaker interface { Speak() string } type Dog struct {} func (d Dog) speak() string { return "Woof" } has lowercase speak(), so it does not satisfy interface. type Speaker interface { Speak() string } type Dog struct {} func Speak(d Dog) string { return "Woof" } defines a function, not a method. type Speaker interface { Speak() string } type Dog struct {} func (d *Dog) Speak() int { return 1 } has wrong return type int.

3. Final Answer:

   type Speaker interface { Speak() string } type Dog struct {} func (d Dog) Speak() string { return "Woof" } -> Option B

4. Quick Check:

   Method name and signature must match exactly [OK]

Hint: Method name and signature must match interface exactly [OK]

Common Mistakes:

• Using lowercase method names
• Defining functions instead of methods
• Mismatching return types

3. What will be the output of the following Go program?

package main
import "fmt"

type Reader interface {
  Read() string
}

type File struct {}
func (f File) Read() string {
  return "file content"
}

func printContent(r Reader) {
  fmt.Println(r.Read())
}

func main() {
  f := File{}
  printContent(f)
}

medium

A. No output

B. Compilation error: File does not satisfy Reader

C. file content

D. Runtime panic

Solution

1. Step 1: Check if File satisfies Reader interface

   File has method Read() string, so it satisfies Reader.

2. Step 2: Trace function call and output

   In main, f is passed to printContent, which calls Read() and prints "file content".

3. Final Answer:

   file content -> Option C

4. Quick Check:

   Interface satisfied, method called, prints string [OK]

Hint: Check method presence to confirm interface satisfaction [OK]

Common Mistakes:

• Assuming explicit declaration needed
• Confusing method receiver types
• Expecting runtime errors without cause

4. Identify the error in the following Go code that prevents Car from satisfying the Vehicle interface:

package main
import "fmt"

type Vehicle interface {
  Drive()
}

type Car struct {}
func (c *Car) Drive() {
  fmt.Println("Driving")
}

func main() {
  var v Vehicle
  c := Car{}
  v = c
  v.Drive()
}

medium

A. Car does not satisfy Vehicle because Drive has pointer receiver but v is assigned a value.

B. Drive method has wrong return type.

C. Vehicle interface requires Drive with parameters.

D. No error, code runs fine.

Solution

1. Step 1: Check method receiver type

   Drive is defined with pointer receiver (*Car), so only *Car satisfies Vehicle, not Car value.

2. Step 2: Check assignment in main

   Variable v is assigned c which is a value, not pointer, causing mismatch.

3. Final Answer:

   Car does not satisfy Vehicle because Drive has pointer receiver but v is assigned a value. -> Option A

4. Quick Check:

   Pointer receiver methods require pointer type for interface satisfaction [OK]

Hint: Pointer receiver methods need pointer type to satisfy interface [OK]

Common Mistakes:

• Assigning value instead of pointer to interface
• Ignoring receiver type in method
• Assuming method signature mismatch

5. Given the interface and types below, which assignment will cause a compile-time error due to interface satisfaction rules?

type Writer interface {
  Write(data string) error
}

type Logger struct {}
func (l Logger) Write(data string) error {
  return nil
}

type FileWriter struct {}
func (f *FileWriter) Write(data string) error {
  return nil
}

var w Writer

// Which assignment is invalid?
// A) w = Logger{}
// B) w = &Logger{}
// C) w = FileWriter{}
// D) w = &FileWriter{}

hard

A. w = &FileWriter{}

B. w = &Logger{}

C. w = Logger{}

D. w = FileWriter{}

Solution

1. Step 1: Analyze Logger methods

   Logger has Write with value receiver, so both Logger and *Logger satisfy Writer.

2. Step 2: Analyze FileWriter methods

   FileWriter has Write with pointer receiver, so only *FileWriter satisfies Writer, not FileWriter value.

3. Step 3: Check assignments

   Assignment C tries to assign FileWriter{} value to Writer, which is invalid.

4. Final Answer:

   w = FileWriter{} causes compile-time error due to missing method on value receiver. -> Option D

5. Quick Check:

   Pointer receiver methods require pointer type for interface [OK]

Hint: Pointer receiver methods need pointer type for interface satisfaction [OK]

Common Mistakes:

• Assigning value type when method has pointer receiver
• Assuming pointer and value types are interchangeable
• Ignoring method receiver type