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Defining Custom Types

Part of the Fundamentals section of Coddy's GO journey — lesson 94 of 109.

In Go, you can create your own custom types based on existing types. This gives your code more clarity and type safety.

Define a custom type for temperature in Celsius:

type Celsius float64

func main() {
    var temperature Celsius = 25.5
    fmt.Printf("Temperature: %.1f°C\n", temperature)
}

The result shows the temperature value:

Temperature: 25.5°C

Custom types behave like their underlying types but are treated as distinct types by the compiler, improving code readability and preventing logical errors.

Challenge

Beginner

In this challenge, you'll practice defining a custom type in Go. Custom types allow you to create your own data types based on existing ones.

Your task is to define a custom type called Temperature that is based on float64, and then create a variable of this type.

After defining the type, the program should print the value and type of the temperature variable.

Try it yourself

package main

import "fmt"

// TODO: Define a custom type called 'Temperature' based on float64

func main() {
	// Create a variable of type Temperature with value 23.5
	var roomTemp Temperature = 23.5
	
	// Print the value and type of roomTemp
	fmt.Printf("Room temperature: %v\n", roomTemp)
	fmt.Printf("Type of roomTemp: %T\n", roomTemp)
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction to Go

What is Go?Hello World Println Go Comments

4Comparison & Logical Operators

Comparison Operators - Part 1 Comparison Operators - Part 2 Logical AND Operator Logical OR Operator Logical NOT Operator Operator Precedence Basics Recap - Making Comparisons

7Control Flow: Loops

What The `for` Loop Explained For Loop - Basic For Loop - Condition Only The `break` Keyword The `continue` Keyword Nested Loops Recap - Repeating Actions

10Composite Types: Arrays

Introduction to Arrays Declaring Arrays Initializing Arrays Accessing Array Elements Array Length with `len`Iterating Over Arrays Multi-dimensional Arrays

13Composite Types: Structs

Defining Custom TypesCreating Struct Instances Accessing Struct Fields Pointers to Structs Initializing Structs Embedded Structs Anonymous Structs Recap - Custom Data Structures

2Variables and Basic Data Types

What is a variable Type Inference with `:=`Integers (int)Floating-Point Numbers Booleans Strings Zero Values Constants Naming Conventions Recap - Variables and Types

5Basic Input/Output

Formatted Output Format Verbs Printing Types Getting Basic User Input Recap - Input and Output

8Functions

Understanding Functions Declaring a Function Calling Functions Function Parameters Returning a Single Value Returning Multiple Values Named Return Values Function Scope Basics Recap - Creating Reusable Code

11Composite Types: Slices

Introduction to Slices Declaring Slice Literals Creating Slices with `make`Slice Length vs Capacity Accessing Slice Elements Appending Elements Slicing Existing Slices/Arrays Iterating Over Slices Copying Slices Recap - Dynamic Lists

14Basic Error Handling

The Concept of Errors The `error` Interface Functions Returning Errors Checking for Errors Creating Simple Errors Creating Formatted Errors Basic Error Handling Recap - Handling Problems