1. What It Is and Why You Need It

The errors library is a standard package of the Go language, providing basic functions for creating, formatting, and handling errors. Unlike many other languages where exceptions are the primary error handling mechanism, Go uses explicit return of error values from functions. This makes the program's execution flow more predictable and controllable.

The main task of the library is to provide a simple and efficient way to create new errors, compare their types, and add contextual information (e.g., "wrapping" errors). In Go, an error is simply the error interface, which any type with an Error() string method implements. This provides enormous flexibility: you can create your own error types with additional fields (error code, request data, etc.).

Why is it needed? Without it, it's impossible to write a reliable Go application. Every time a function can fail (working with files, network, database), it returns an error. Ignoring errors (assigning them to the _ variable) is considered bad practice. The errors library allows you not only to report what went wrong but also to build an error chain so that during debugging you know exactly at which stage the failure occurred.

2. Installation

The errors package is part of the Go standard library. This means that no additional installation is required. It is available "out of the box" when you install any Go SDK. To use it, simply import it into your code:

import "errors"

If you are using Go Modules (the standard since Go 1.11+), the package will be automatically available. No go get commands are needed for the standard library.

Important: There is also a popular third-party library github.com/pkg/errors that provides extended functionality (call stacks, formatting). However, in this article, we focus exclusively on the standard errors package, which is the foundation for any error handling in Go.

3. Quick Start

A minimal working example of creating and handling an error:

package main\n\nimport (\n    "errors"\n    "fmt"\n)\n\n// Function that divides two numbers. If the divisor is zero, it returns an error.\nfunc divide(a, b float64) (float64, error) {\n    if b == 0 {\n        return 0, errors.New("division by zero is not possible")\n    }\n    return a / b, nil\n}\n\nfunc main() {\n    result, err := divide(10, 2)\n    if err != nil {\n        fmt.Println("Error:", err)\n    } else {\n        fmt.Println("Result:", result)\n    }\n\n    // Try with an error\n    result2, err2 := divide(10, 0)\n    if err2 != nil {\n        fmt.Println("Error:", err2) // Output: Error: division by zero is not possible\n    } else {\n        fmt.Println("Result:", result2)\n    }\n}

In this example, we created a simple error using errors.New() and checked for its presence using the standard if err != nil pattern.

4. Main Functions and Methods

Below are 8 key functions/methods of the errors package with detailed descriptions and examples.

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4.1 errors.New(text string) error

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Signature: func New(text string) error

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