Why is "no early returns" not a good rule?

I do early returns in code I write, but ONLY because everybody seems to do it. I prefer stuff to be in predictable places: variables at the top, return at the end. Simpler? Delphi/Pascal style.

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jandrewrogers 2 days ago | parent | next [-]

Early returns makes the code more linear, reduces conditional/indent depth, and in some cases makes the code faster. In short, it often makes code simpler. The “no early returns” is a soft version of “no gotos”. There are cases where it is not possible to produce good code while following those heuristics. A software engineer should strive to produce the best possible code, not rigidly follow heuristics even when they don’t make sense.

There is an element of taste. Don’t create random early returns if it doesn’t improve the code. But there are many, many cases where it makes the code much more readable and maintainable.

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SideburnsOfDoom 2 days ago | parent | prev | next [-]

The "no early returns" rule came about because was a good rule in context, specifically C and FORTRAN code before roughly 1990. It was part of "structured programming", contemporary to "Go To Statement Considered Harmful", Dijkstra, 1968. And it became received wisdom - i.e. a rule that people follow without close examination.

For example of the rule, a function might allocate, do something and then de-allocate again at the end of the block. A second exit point makes it easy to miss that de-allocation, and so introduce memory leaks that only happen sometimes. The code is harder to reason about and the bugs harder to find.

source:

> A problem with early exit is that cleanup statements might not be executed. ... Cleanup must be done at each return site, which is brittle and can easily result in bugs.

https://en.wikipedia.org/wiki/Structured_programming#Early_r...

About 90% of us will now be thinking "but that issue doesn't apply to me at all in $ModernLang. We have GC, using (x) {} blocks, try-finally, or we have deterministic finalisation, etc."

And they're correct. In most modern languages it's fine. The "no early returns" rule does not apply to Java, TypeScript, C#, Rust, Python, etc. Because these languages specifically made early return habitable.

The meta-rule is that some rules persist past the point when they were useful. Understand what a rule is for and then you can say when it applies at all. Rules without reasons make this harder. Some rules have lasted: we typically don't use goto at all any more, just structured wrappers of it such as if-else and foreach

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zahlman 2 days ago | parent [-]

> And they're correct. In most modern languages it's fine. The "no early returns" rule does not apply to Java, TypeScript, C#, Rust, Python, etc. Because these languages specifically made early return habitable.

Early return is perfectly manageable in C as long as you aren't paranoid about function inlining. You just have a wrapper that does unconditional setup, passes the acquired resources to a worker, and unconditionally cleans up. Then the worker can return whenever it likes, and you don't need any gotos either.

	▲	SideburnsOfDoom 2 days ago \| parent [-]
		> In C, you just have a wrapper that does unconditional setup, passes the acquired resources to a worker, and unconditionally cleans up. Then the worker can return whenever it like Right, so you allow early return only in functions that do not have any setup and clean-up - where it's safe. Something like "pure" functions. And you describe a way to extract such functions from others.

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mrgaro 2 days ago | parent | prev | next [-]

I remember having this argument with my professor at the school, who insisted that a function should have only one "return" clause at the very end. Even as I tried, I could not get him to explain why this would be valuable and how does this produce better code, so I'm interested on hearing your take on this?

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superxpro12 2 days ago | parent [-]

It helps prevent bugs with state. The apple login bypass bug comes to mind.

Basically, you have code in an "if" statement, and if you return early in that if statement, you might have code that you needed to run, but didnt.

Forcing devs to only "return once" encourages the dev to think through any stateful code that may be left in an intermediate state.

In practice, at my shop, we permit early returns for trivial things at the top of a function, otherwise only one return at the bottom. That seems to be the best of both worlds for this particular rule.

	▲	SideburnsOfDoom 2 days ago \| parent \| next [-]
		> The apple login bypass bug comes to mind. I think you're talking about this "goto fail" bug? https://teamscale.com/blog/en/news/blog/gotofail > In practice, at my shop, we permit early returns for trivial things Are you also writing C or similar? If so, then this rule is relevant. In modern languages, there are language constructs to aid the cleanup on exit, such as using(resource) {} or try {} finally {} It really does depend on if these conveniences are available or not. For the rest of us, the opposite of "no early return" is to choose early return only sometime - in cases where results in better code, e.g. shorter, less indented and unlikely to cause issues due to failure to cleanup on exit. And avoid it where it might be problematic. In other words, to taste. > Kent Beck, Martin Fowler, and co-authors have argued in their refactoring books that nested conditionals may be harder to understand than a certain type of flatter structure using multiple exits predicated by guard clauses. Their 2009 book flatly states that "one exit point is really not a useful rule. Clarity is the key principle: If the method is clearer with one exit point, use one exit point; otherwise don’t". https://en.wikipedia.org/wiki/Structured_programming#Early_e... this thinking is quite different to say, 25 years earlier than that, and IMHO the programming language constructs available play a big role.
	▲	Symmetry 2 days ago \| parent \| prev \| next [-]
		The rule of thumb I use is to only have one return after modifying state that will persist outside the function call.
	▲	mrgaro a day ago \| parent \| prev [-]
		Thank you!

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katzenversteher 2 days ago | parent | prev | next [-]

For me it's mostly about indentation / scope depth. So I prefer to have some early exits with precondition checks at the beginning, these are things I don't have to worry about afterwards and I can start with the rest at indentation level "0". The "real" result is at the end.

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stonemetal12 2 days ago | parent | prev | next [-]

Because good code checks pre conditions and returns early if they are not met.

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dragonwriter 2 days ago | parent | prev [-]

> Why is "no early returns" not a good rule?

It might be a good guideline.

Its not a good rule because slavishly following results in harder to follow code written to adhere to it.