People have been arguing about how to indent code for as long as there’s been code, and nobody has settled it. Java’s Checkstyle aligns continuations under the open paren, ESLint and Prettier each invent their own rules, Go’s gofmt uses tabs and shrugs, RuboCop hands you a menu, Python’s PEP 8 picks four spaces and leaves the rest to taste. Every tool has its own dialect, and teams waste hours fighting over the details. I suggest a simple rule of monotonic indentation for source code of any programming language:
Between any two adjacent lines, indentation may increase by exactly one unit.
This rule should resolve most disputes about code formatting style. It is easy to add as an extra check to any existing style checker, or to deploy on its own as a small standalone tool.
According to the rule, this Java code is illegal:
class Repository {
void save(File file,
String text, String summary,
boolean overwrite) {
if (file.exists()
&& !overwrite) {
throw new IllegalStateException(
"file already exists");
}
update(file,
text,
summary);
}
}
This one is legal (and pretty, if you ask me):
class Repository {
→→void save(File file,
→→String text, String summary,
boolean overwrite) {
if (file.exists()
→→&& !overwrite) {
throw new IllegalStateException(
→→"file already exists");
}
update(file,
→→text,
summary);
}
}
The idea is simple: going down the code, you may step right by one notch at a time, but you may jump back left by as many notches as you want. You can’t skip steps on the way in, but you can leap out freely. Every line still lands on a grid, never in between.
Together with the Paired Brackets rule, this makes the code look ideal: brackets line up vertically and indentation never jumps further than necessary.
BTW, the parser of EO, our experimental language, enforces this rule syntactically. This is similar to the off-side rule of Python, where indentation defines block structure rather than braces. However, in EO everything is an object, while in Python it is not. That’s why EO can afford to be stricter and demand monotonic steps everywhere.
