oopIn most cases (maybe even in all of them), if-then-else can and must be replaced by a decorator or simply another object. I’ve been planning to write about this for almost a year but only today found a real case in my own code that perfectly illustrates the problem. So it’s time to demonstrate it and explain.
Take a look at the class DyTalk from yegor256/rultor and its method modify(). In a nutshell, it prevents you from saving any data to the DynamoDB if there were no modifications of the XML document. It’s a valid case, and it has to be validated, but the way it’s implemented is simply wrong. This is how it works (an oversimplified example):
class DyTalk implements Talk {
void modify(Collection<Directive> dirs) {
if (!dirs.isEmpty()) {
// Apply the modification
// and save the new XML document
// to the DynamoDB table.
}
}
}
What’s wrong, you wonder? This if-then-else forking functionality doesn’t really belong to this object—that’s what’s wrong. Modifying the XML document and saving it to the database is its functionality, while not saving anything if the modification instructions set is empty is not (it’s very similar to defensive programming). Instead, there should be a decorator, which would look like this:
class QuickTalk implements Talk {
private final Talk origin;
void modify(Collection<Directive> dirs) {
if (!dirs.isEmpty()) {
this.origin.modify(dirs);
}
}
}
Now, if and when we need our talk to be more clever in situations where the list of directives is empty, we decorate it with QuickTalk. The benefits are obvious: the DyTalk class is smaller and therefore more cohesive.
But the question is bigger than just that. Can we make a rule out of it? Can we say that each and every forking is bad and should be moved out of a class? What about forking that happens inside a method and can’t be converted to a decorator?
I’m suggesting this simple rule: If it’s possible to convert if-then-else forking to a decorator, it has to be done. If it’s not done, it’s a code smell. Make sense?
