Go - lesson 3 | HackIndia Skills

Key point

One idea

In Go, a type implements an interface by having the methods the interface asks for. You do not write “implements”.

This means your service can depend on behavior, such as “can find a student”, instead of a concrete detail, such as “uses Postgres”.

Why it matters

Your HackIndia repo needs typed handlers and clean design. Interfaces help you keep HTTP code separate from storage code.

A recruiter should be able to read your handler and see the business action. They should not need to understand your map, file, or database code first.

Your to-do

Design the interface

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Start from the handler use case, not the storage package.
Name the interface by behavior, such as StudentStore or ProjectFinder.
Keep it small. One or two methods is fine.
Accept and return your own types from lesson 2.
Put the interface near the code that uses it, unless many packages share it.

0 of 5 done

Example

Small store example

Here the handler depends on StudentStore. The mapStore type matches it because it has FindByID with the same signature.

No extra keyword is needed. If the method is missing or has the wrong return type, the code will not compile.

package main

import "fmt"

type Student struct {
	ID   string
	Name string
}

type StudentStore interface {
	FindByID(id string) (Student, bool)
}

type mapStore struct {
	students map[string]Student
}

func (m mapStore) FindByID(id string) (Student, bool) {
	student, ok := m.students[id]
	return student, ok
}

func PrintStudent(store StudentStore, id string) {
	student, ok := store.FindByID(id)
	if !ok {
		fmt.Println("student not found")
		return
	}
	fmt.Println(student.Name)
}

func main() {
	store := mapStore{
		students: map[string]Student{
			"101": {ID: "101", Name: "Asha"},
		},
	}

	PrintStudent(store, "101")
}

Tip

Use fakes

Interfaces make testing easier. You can pass a fake store to a handler instead of connecting to a real database or editing live data.

For a college project, this is enough to show good backend thinking. Your README can say the HTTP layer is tested with a fake store.

type fakeStore struct{}

func (fakeStore) FindByID(id string) (Student, bool) {
	return Student{ID: id, Name: "Test Student"}, true
}

Common mistake

Avoid empty interface

Do not use interface{} because you are unsure of the type. It means any non-interface type can fit, so you lose useful compiler checks.

Prefer concrete types or a small interface with named methods. Your service will be easier to read and safer to change.

Go 1.27 note

Go 1.27 supports generic methods, so older tutorials saying Go has no generic methods are outdated.

But interface methods may not declare type parameters, and generic methods cannot implement interface methods. Keep service interfaces simple and non-generic.