Interface definition in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an interface named Speaker.

Go

type Speaker [1] {
    Speak() string
}

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

Afunc

Bstruct

Cinterface

Dpackage

Attempts:

3 left

💡 Hint

Common Mistakes

Using struct instead of interface to define an interface.

Forgetting the keyword interface.

The keyword interface is used to define an interface in Go.

2fill in blank

medium

Complete the code to declare a method Speak() that returns a string in the interface.

Go

type Speaker interface {
    [1]() string
}

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

ASpeak

BListen

CSay

DTalk

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name than defined in the interface.

Adding parameters to the method when none are required.

The method name in the interface is Speak which returns a string.

3fill in blank

hard

Fix the error in the interface definition by completing the code.

Go

type [1] interface {
    Speak() string
}

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

ASpeaker

Bspeaker

CSpeakers

DSpeak

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for exported interfaces.

Using method names as interface names.

Interface names in Go are usually capitalized and descriptive. Here, Speaker is the correct name.

4fill in blank

hard

Fill both blanks to define an interface named Reader with a method Read that returns an int and an error.

Go

type [1] interface {
    [2]() (int, error)
}

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

AReader

BWriter

CRead

DWrite

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing interface and method names.

Incorrect method signature.

The interface is named Reader and the method is Read which returns an int and an error.

5fill in blank

hard

Fill all three blanks to define an interface named Writer with a method Write that takes a byte slice and returns an int and an error.

Go

type [1] interface {
    [2]([3] []byte) (int, error)
}

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

AWriter

BWrite

Cdata

DRead

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method or parameter names.

Wrong parameter types.

The interface is Writer, the method is Write, and the parameter name is data which is a byte slice.

Practice

1. What does an interface in Go define?

easy

A. A concrete type with fields and methods

B. A variable that holds data

C. A set of method signatures without implementation

D. A function that returns multiple values

Solution

1. Step 1: Understand what an interface is

   An interface in Go specifies method signatures but does not provide their implementation.

2. Step 2: Differentiate from other types

   Concrete types have fields and method implementations, unlike interfaces.

3. Final Answer:

   A set of method signatures without implementation -> Option C

4. Quick Check:

   Interface = method signatures only [OK]

Hint: Interfaces list methods only, no code inside [OK]

Common Mistakes:

• Thinking interfaces hold data
• Confusing interfaces with structs
• Assuming interfaces implement methods

2. Which of the following is the correct syntax to define an interface named Shape with a method Area() returning a float64?

easy

A. func Shape interface { Area() float64 }

B. interface Shape { func Area() float64 }

C. type Shape struct { Area() float64 }

D. type Shape interface { Area() float64 }

Solution

1. Step 1: Recall Go interface syntax

   Interfaces are defined with the keyword type, name, then interface and method signatures inside braces.

2. Step 2: Check each option

   type Shape interface { Area() float64 } matches correct syntax. Options B, C, and D misuse keywords or structure.

3. Final Answer:

   type Shape interface { Area() float64 } -> Option D

4. Quick Check:

   Correct interface syntax = type Shape interface { Area() float64 } [OK]

Hint: Use 'type Name interface { methods }' for interfaces [OK]

Common Mistakes:

• Using 'interface' keyword alone without 'type'
• Defining methods inside struct instead of interface
• Placing 'func' keyword inside interface method

3. What will be the output of this Go code?

package main
import "fmt"
type Printer interface {
    Print()
}
type Document struct {
    content string
}
func (d Document) Print() {
    fmt.Println(d.content)
}
func main() {
    var p Printer
    d := Document{"Hello, Go!"}
    p = d
    p.Print()
}

medium

A. Runtime panic: nil pointer dereference

B. Hello, Go!

C. Compilation error: cannot assign Document to Printer

D. No output

Solution

1. Step 1: Check interface implementation

   Document has a method Print() matching Printer interface, so Document implements Printer.

2. Step 2: Assign and call method

   Variable p of type Printer is assigned d (Document), then p.Print() calls Document.Print(), printing content.

3. Final Answer:

   Hello, Go! -> Option B

4. Quick Check:

   Interface method calls concrete method [OK]

Hint: Assign concrete type with matching methods to interface [OK]

Common Mistakes:

• Thinking interface needs explicit implementation declaration
• Expecting compile error on assignment
• Assuming interface variable is nil

4. Identify the error in this Go code snippet:

type Reader interface {
    Read(p []byte) (n int, err error)
}
type File struct {}
func (f File) Read() (int, error) {
    return 0, nil
}

medium

A. Method Read has wrong signature, missing parameter

B. File does not implement Reader because it lacks Read method

C. Interface Reader cannot have methods with parameters

D. No error, code is correct

Solution

1. Step 1: Compare method signatures

   Reader interface expects Read with parameter []byte and two return values.

2. Step 2: Check File's Read method

   File's Read method has no parameters, so signature does not match interface.

3. Final Answer:

   Method Read has wrong signature, missing parameter -> Option A

4. Quick Check:

   Method signature must match interface [OK]

Hint: Method signatures must exactly match interface methods [OK]

Common Mistakes:

• Ignoring method parameters in implementation
• Assuming method name alone is enough
• Thinking interface methods can't have parameters

5. Given these interfaces and types:

type Reader interface {
    Read(p []byte) (n int, err error)
}
type Writer interface {
    Write(p []byte) (n int, err error)
}
type ReadWriter interface {
    Reader
    Writer
}
type MyFile struct {}
func (f MyFile) Read(p []byte) (int, error) {
    return len(p), nil
}
func (f MyFile) Write(p []byte) (int, error) {
    return len(p), nil
}

Which statement is true about MyFile and ReadWriter?

hard

A. MyFile implements ReadWriter because it has both Read and Write methods

B. MyFile only implements Reader, not ReadWriter

C. MyFile does not implement any interface

D. ReadWriter cannot embed other interfaces

Solution

1. Step 1: Understand interface embedding

   ReadWriter embeds Reader and Writer, so it requires both methods.

2. Step 2: Check MyFile methods

   MyFile has both Read and Write methods matching signatures.

3. Step 3: Confirm implementation

   Since MyFile has all required methods, it implements ReadWriter.

4. Final Answer:

   MyFile implements ReadWriter because it has both Read and Write methods -> Option A

5. Quick Check:

   Embedded interfaces require all methods [OK]

Hint: Embedded interfaces combine methods; implement all to satisfy [OK]

Common Mistakes:

• Thinking embedding interfaces is invalid
• Assuming partial method implementation suffices
• Confusing interface embedding with inheritance