Hands-On Software Engineering with Golang

Questions

1. What do the SOLID acronym initials stand for?
2. Why does the following piece of code violate the SRP? How would you refactor it to make sure it doesn't violate it?

import (
    "crypto/ecdsa"
)

type Document struct { //... }

// Append adds a line to the end of the document.
func (d *Document) Append(line string) { //...  }

// Content returns the document contents as a string.
func (d *Document) Content() string { //... }

// Sign calculates a hash for the document contents, signs it with the
// provided private key and returns back the result.
func (d *Document) Sign(pk *ecdsa.PrivateKey) (string, error) { //... }

3. What is the main concept behind the ISP? Discuss how would you apply it to improve the following function signature: