Hands-On Software Engineering with Golang

Chapter 2

1. The following is what the SOLID acronym initials stand for:
   • Single responsibility
   • Open/Closed
   • Liskov substitution
   • Interface segregation
   • Dependency inversion
2. The code conflates two responsibilities: retrieving/mutating the state of a document and creating a signature for the document's content. Furthermore, the proposed implementation is inflexible as it forces the use of a specific signing algorithm. To address this problem, we can remove the Sign method from the Document type and provide an external helper that can sign not only instances of Document but also any type that can export its content as a string:

type ContentProvider interface {
    Content() string
}

type ECDADocumentSigner struct {//...}

func (s ECDADocumentSigner) ...