JCjcrites·Feb 19, 2018
Totally agree with the concerns of the article. When you have to write a class of comparison functions like this in many types, it's arguably a violation of the Don't Repeat Yourself (DRY) principle to implement comparison with unique, bespoke code in each type. Scenarios like this beg for a library or type system to make things easier.
In Java's case, a better solution is Guava's ComparisonChain:
public int compareTo(Foo that) {
return ComparisonChain.start()
.compare(this.aString, that.aString)
.compare(this.anInt, that.anInt)
.compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
.result();
}
There are similar utility methods for computing the object hashCode() and toString() and so on. See: https://github.com/google/guava/wiki/CommonObjectUtilitiesEx...
There's still an opp
Read the rest
ortunity to make mistakes like typos here, but due to the visual consistency it's less likely. Actual logic errors in the comparison are also less likely.
A more powerful language than Java could potentially automate the entire implementation of methods like these (rather than just some of it), by reflecting over the set of fields in a class. Apache Lombok's annotations can kind of do this for a number of common boilerplate methods, though it looks like not yet for compareTo(): https://projectlombok.org/features/Data
C# properties are an example of an improvement over Java, for example, but C# class implementors are still responsible for dealing with implementing Equals(), GetHashCode(), and ToString() just like Java, as far as I know.
I would be interested to hear if there are any current programming languages that handle this use-case particularly well. Any Haskell, F#, or Scala folks out there who can comment?