Small Go interfaces example: proof of identity cards

This tutorial demonstrates Go interfaces for beginners. We'll create a ProofOfId interface defining methods for identity documents (ID card, driver's license, passport) and a CountriesList interface for listing countries. This illustrates how interfaces function as a form of polymorphism, replacing inheritance in other languages.

Project Setup

1. Create a project directory: mkdir proof-of-identity-checker && cd proof-of-identity-checker
2. Initialize a Go module: go mod init <yourname>/proof-of-identity-checker (replace <yourname> with your name or a suitable identifier).
3. Open the directory in your code editor.

Defining Interfaces (interfaces.go)

package main

import "time"

type ProofOfId interface {
    getExpDate() time.Time
    getName() string
    getObtentionDate() time.Time
}

type CountriesList interface {
    getCountries() []string
}

ProofOfId requires getExpDate(), getName(), and getObtentionDate(). CountriesList requires getCountries().

Interface-Based Functions (main.go)

package main

import "time"

// IdentityVerification checks if a proof of ID is valid (date-based).
func IdentityVerification(proof ProofOfId) bool {
    // ... (Date comparison logic would go here.  See the provided link for details.)
    return proof.getExpDate().After(time.Now()) //Example: Check if expiration date is in the future.
}

// DisplayVisitedCountries prints a list of visited countries.
func DisplayVisitedCountries(passport CountriesList) {
    countries := passport.getCountries()
    println("Visited countries:")
    for _, country := range countries {
        println(country)
    }
}

Implementing Identity Document Types

• Identification Card (idcard.go)

package main

import "time"

type IdCard struct {
    Name          string
    ObtentionDate time.Time
    ExpDate       time.Time
}

func (card IdCard) getName() string {
    return card.Name
}

func (card IdCard) getExpDate() time.Time {
    return card.ExpDate
}

func (card IdCard) getObtentionDate() time.Time {
    return card.ObtentionDate
}

• Driver's License (driver-license.go)

package main

import "time"

type DriverLicense struct {
    Name          string
    ObtentionDate time.Time
    ExpDate       time.Time
    Enterprise    string
}

func (license DriverLicense) getName() string {
    return license.Name
}

func (license DriverLicense) getExpDate() time.Time {
    return license.ExpDate
}

func (license DriverLicense) getObtentionDate() time.Time {
    return license.ObtentionDate
}

func (license DriverLicense) getEnterprise() string {
    return license.Enterprise
}

• Passport (passport.go)

package main

import "time"

type Passport struct {
    Name             string
    ObtentionDate    time.Time
    ExpDate          time.Time
    VisitedCountries []string
}

func (passport Passport) getName() string {
    return passport.Name
}

func (passport Passport) getExpDate() time.Time {
    return passport.ExpDate
}

func (passport Passport) getObtentionDate() time.Time {
    return passport.ObtentionDate
}

func (passport Passport) getCountries() []string {
    return passport.VisitedCountries
}

Testing (main.go continued)

func main() {
    idCard := IdCard{ObtentionDate: time.Now().Add(24 * time.Hour), ExpDate: time.Now().Add(730 * 24 * time.Hour)}
    driverLicense := DriverLicense{ObtentionDate: time.Now().Add(-24 * time.Hour), ExpDate: time.Now().Add(365 * 24 * time.Hour)}
    passport := Passport{ObtentionDate: time.Now().Add(-24 * time.Hour), ExpDate: time.Now().Add(-1 * time.Hour), VisitedCountries: []string{"France", "Spain", "Belgium"}}

    println(IdentityVerification(idCard))
    println(IdentityVerification(driverLicense))
    println(IdentityVerification(passport))

    DisplayVisitedCountries(passport)
}

Run with go run .

Conclusion

This example shows how Go interfaces enable flexible code by defining contracts between objects, promoting code reusability and maintainability. The provided link for date comparison should be consulted to complete the IdentityVerification function's date checking logic.

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