From date should be lower than to date

TL;DR: Intervals are there. Why use plain dates?

Problems

• Missing abstraction

• Duplicated Code

• Not enforced invariants

• Primitive Obsession

• Bijection Fault

• Fail Fast principle violation

Solutions

1. Create and use an Interval Object

Context

The restriction "From date should be lower than to date" means that the starting date of a certain interval should occur before the ending date of the same interval.

The "From date" should be a date that comes earlier in time than the "To date".

This restriction is in place to ensure that the interval being defined makes logical sense and that the dates used to define it are in the correct order.

We all know it. But we miss creating the Interval object.

Would you create a Date as a pair of 3 Integer numbers? Certainly, not.

This is the same.

Sample Code

Wrong

val from = LocalDate.of(2018, 12, 9)
val to = LocalDate.of(2022, 12, 22)

val elapsed = elapsedDays(from, to)

fun elapsedDays(fromDate: LocalDate, toDate: LocalDate): Long {
    return ChronoUnit.DAYS.between(fromDate, toDate)
}

// We need to apply this short function 
// Or the inline version many times in our code
// We don't check from Date to be less than toDate
// We can make accounting numbers with a negative number

Right

// We reify the Interval Concept

data class Interval(val fromDate: LocalDate, val toDate: LocalDate) {
    init {
        if (fromDate >= toDate) {
            throw IllegalArgumentException("From date must be before to date")
        }
        // Of course the Interval must be immutable
        // By using the keyword 'data'
    }

    fun elapsedDays(): Long {
        return ChronoUnit.DAYS.between(fromDate, toDate)
    }
}

val from = LocalDate.of(2018, 12, 9)
val to = LocalDate.of(2002, 12, 22)

val interval = Interval(from, to) // Invalid

Detection

[X] Manual

This is a primitive obsession smell.

It is related to how we model things.

Tags

• Primitive

Conclusion

If you find software with missing simple validations, it certainly needs reification.

Relations

Code Smell 177 - Missing Small Objects

Maxi Contieri ・ Nov 5 '22

#webdev #javascript #beginners #programming

Code Smell 46 - Repeated Code

Maxi Contieri ・ Dec 8 '20

#oop #codenewbie #tutorial #webdev

Code Smell 122 - Primitive Obsession

Maxi Contieri ・ Mar 17 '22

#oop #webdev #tutorial #beginners

More Info

Fail Fast

Maxi Contieri ・ Dec 6 '20

#codenewbie #programming #webdev #oop

Disclaimer

Code Smells are just my opinion.

Credits

Photo by Towfiqu barbhuiya on Unsplash

At any particular point in time, the features provided by our programming languages reflect our understanding of software and programming.

R. E. Fairley

Software Engineering Great Quotes

Maxi Contieri ・ Dec 28 '20

#codenewbie #programming #quotes #software

This article is part of the CodeSmell Series.

How to Find the Stinky parts of your Code

Maxi Contieri ・ May 21 '21

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