Interface Segregation Principle

~ What ? ~

Our modules should need to know about functionality they don’t use.

We need to split our modules into smaller abstractions, like interfaces.

Example

interface Flyer {
	fly();
}
interface Animal {
	speak();
}
 
class Bird implements Flyer, Animal {}

// Interface representing a document that can be opened, saved, and printed
interface Document {
    open(): void;
    save(): void;
    print(): void;
}
 
// Interface representing a document that can be edited
interface EditableDocument {
    edit(): void;
}
 
// Interface representing a document that can be shared
interface ShareableDocument {
    share(): void;
}
 
// Class implementing the Document interface
class TextDocument implements Document, EditableDocument, ShareableDocument {
    open(): void {
        console.log("Opening text document...");
    }
 
    save(): void {
        console.log("Saving text document...");
    }
 
    print(): void {
        console.log("Printing text document...");
    }
 
    edit(): void {
        console.log("Editing text document...");
    }
 
    share(): void {
        console.log("Sharing text document...");
    }
}
 
// Class implementing the Document interface
class SpreadsheetDocument implements Document, EditableDocument {
    open(): void {
        console.log("Opening spreadsheet document...");
    }
 
    save(): void {
        console.log("Saving spreadsheet document...");
    }
 
    print(): void {
        console.log("Printing spreadsheet document...");
    }
 
    edit(): void {
        console.log("Editing spreadsheet document...");
    }
}
 
// Function demonstrating usage of Document interface
function processDocument(doc: Document) {
    doc.open();
    doc.save();
    doc.print();
}
 
// Usage
const textDoc = new TextDocument();
const spreadsheetDoc = new SpreadsheetDocument();
 
processDocument(textDoc); // Open, save, and print text document
processDocument(spreadsheetDoc); // Open, save, and print spreadsheet document