Defining structs in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a struct in Go?

A struct in Go is a way to group related data together into a single unit, like a container with named fields. It helps organize information about something, like a person or a car.

beginner

How do you define a struct type in Go?

You use the keyword type followed by the struct name and the keyword struct with fields inside curly braces. For example:

type Person struct {
  Name string
  Age  int
}

beginner

How do you create a new struct variable in Go?

You can create a new struct variable by declaring it with the struct type and then filling its fields. For example:

var p Person
p.Name = "Alice"
p.Age = 30

beginner

What is a struct literal in Go?

A struct literal lets you create and fill a struct in one step. For example:

p := Person{Name: "Bob", Age: 25}

This creates a Person with Name "Bob" and Age 25.

intermediate

Can structs in Go have methods?

Yes! You can write functions called methods that work with structs. This helps you add behavior to your data, like making a Person say hello.

Which keyword is used to define a new struct type in Go?

A type

B struct

C class

D var

You use the keyword type to define a new struct type, followed by the struct name and the struct keyword.

How do you access a field named 'Age' in a struct variable 'p'?

A p[Age]

B p->Age

C p.Age

D p.Age()

You access struct fields using dot notation, like p.Age.

What does this code do?

p := Person{Name: "Eve", Age: 22}

A Calls a method on Person

B Creates a Person struct with Name 'Eve' and Age 22

C Defines a new struct type

D Declares a pointer to Person

This is a struct literal creating a Person with the given field values.

Can you add functions that work specifically with a struct type?

A Yes, these are called methods

B No, Go structs cannot have functions

C Only if you use interfaces

D Only with pointers

Go allows you to define methods that are functions tied to a struct type.

Which of these is the correct way to define a struct with fields 'Name' (string) and 'Age' (int)?

A var Person = { Name: string, Age: int }

B struct Person { string Name; int Age }

C class Person { Name: string; Age: int }

D type Person struct { Name string; Age int }

Option D uses correct Go syntax for defining a struct type.

Explain how to define a struct type and create a variable of that type in Go.

Think about how you group data and then use it.

Describe what a struct literal is and how it helps when working with structs.

It's like filling a form all at once.

Practice

1. What is the purpose of defining a struct in Go?

easy

A. To create a new function

B. To group related data fields into a single unit

C. To declare a package

D. To import external libraries

Solution

1. Step 1: Understand the role of structs

   Structs are used to group related data fields together in one unit, like a blueprint for an object.

2. Step 2: Compare with other options

   Functions, packages, and imports serve different purposes unrelated to grouping data.

3. Final Answer:

   To group related data fields into a single unit -> Option B

4. Quick Check:

   Struct = grouped data [OK]

Hint: Structs bundle related info like a real-world object [OK]

Common Mistakes:

• Confusing structs with functions
• Thinking structs declare packages
• Mixing structs with imports

2. Which of the following is the correct way to define a struct named Person with fields Name (string) and Age (int)?

easy

A. type Person { Name string; Age int }

B. struct Person { Name string; Age int }

C. type Person struct { Name string; Age int }

D. Person struct { Name string; Age int }

Solution

1. Step 1: Recall Go struct syntax

   In Go, structs are defined using the syntax: type Name struct { fields }.

2. Step 2: Check each option

   type Person struct { Name string; Age int } matches the correct syntax. Options A, B, and C miss the 'type' keyword or 'struct' keyword placement.

3. Final Answer:

   type Person struct { Name string; Age int } -> Option C

4. Quick Check:

   Correct struct syntax = type Person struct { Name string; Age int } [OK]

Hint: Remember: 'type Name struct { fields }' [OK]

Common Mistakes:

• Omitting 'type' keyword
• Missing 'struct' keyword
• Incorrect order of keywords

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

package main
import "fmt"
type Car struct {
  Brand string
  Year  int
}
func main() {
  c := Car{Brand: "Toyota", Year: 2020}
  fmt.Println(c.Brand)
}

medium

A. Car{Brand: "Toyota", Year: 2020}

B. 2020

C. Compilation error

D. Toyota

Solution

1. Step 1: Understand struct initialization

   The struct Car is initialized with Brand="Toyota" and Year=2020.

2. Step 2: Identify printed field

   The code prints c.Brand, which is "Toyota".

3. Final Answer:

   Toyota -> Option D

4. Quick Check:

   Print c.Brand = Toyota [OK]

Hint: Print field with dot: variable.FieldName [OK]

Common Mistakes:

• Printing the whole struct instead of a field
• Confusing field names
• Expecting Year instead of Brand

4. Identify the error in the following Go code snippet:

package main
import "fmt"
type Book struct {
  Title string
  Pages int
}

func main() {
  b := Book{Title: "Go Guide", Pages: "300"}
  fmt.Println(b)
}

medium

A. Pages field has wrong type, should be int not string

B. Missing import for fmt package

C. Struct fields must be lowercase

D. Cannot print struct directly

Solution

1. Step 1: Check field types in struct initialization

   The Pages field is declared as int but assigned a string "300" which is a type mismatch.

2. Step 2: Verify other possible errors

   Import for fmt package is present. Struct fields can be uppercase. Printing structs directly is allowed.

3. Final Answer:

   Pages field has wrong type, should be int not string -> Option A

4. Quick Check:

   Type mismatch in struct field assignment [OK]

Hint: Match field types exactly when initializing structs [OK]

Common Mistakes:

• Assigning string to int field
• Expecting compilation error from printing struct
• Thinking struct fields must be lowercase

5. Given the struct definition:

type Employee struct {
  Name   string
  Salary int
  Active bool
}

Which of the following code snippets correctly creates a slice of Employee structs with only active employees having salary above 50000?

hard

A. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
var filtered []Employee
for _, e := range emps {
if e.Active && e.Salary > 50000 {
filtered = append(filtered, e)
}
}

B. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
filtered := []Employee{}
for i := range emps {
if emps[i].Salary > 50000 {
filtered = append(filtered, emps[i])
}
}

C. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
filtered := []Employee{}
for _, e := range emps {
if e.Active || e.Salary > 50000 {
filtered = append(filtered, e)
}
}

D. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
filtered := []Employee{}
for _, e := range emps {
if e.Active && e.Salary < 50000 {
filtered = append(filtered, e)
}
}

Solution

1. Step 1: Understand filtering criteria

   We want only employees who are active and have salary above 50000.

2. Step 2: Check each code snippet logic

   emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} var filtered []Employee for _, e := range emps { if e.Active && e.Salary > 50000 { filtered = append(filtered, e) } } uses 'e.Active && e.Salary > 50000' which matches criteria. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} filtered := []Employee{} for i := range emps { if emps[i].Salary > 50000 { filtered = append(filtered, emps[i]) } } misses active check. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} filtered := []Employee{} for _, e := range emps { if e.Active || e.Salary > 50000 { filtered = append(filtered, e) } } uses '||' which includes inactive employees. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} filtered := []Employee{} for _, e := range emps { if e.Active && e.Salary < 50000 { filtered = append(filtered, e) } } uses salary < 50000 which is wrong.

3. Final Answer:

   The code that filters using e.Active && e.Salary > 50000 -> Option A

4. Quick Check:

   Filter with '&&' for both conditions [OK]

Hint: Use && to combine multiple conditions correctly [OK]

Common Mistakes:

• Using || instead of && for filtering
• Ignoring the Active field in filter
• Using wrong salary comparison operator