▲ 129 points

Tiger Style: Coding philosophy (2024)

tigerstyle.dev

by nateb2022·8mo ago·135 comments·view on hn ↗

135 comments

I was enjoying what I was reading until the "Limit function length" part which made me jolt out of my chair.

This is a common misconception.

   Limit function length: Keep functions concise, ideally under 70 lines. Shorter functions are easier to understand, test, and debug. They promote single responsibility, where each function does one thing well, leading to a more modular and maintainable codebase.

Say, you have a process that is single threaded and does a lot of stuff that has to happen step by step.

New dev comes in; and starts splitting everything it does in 12 functions, because, _a function, should do one thing!_ Even better, they start putting stuff in various files because the files are getting too long.

Now you have 12 functions, scattered over multiple packages, and the order of things is all confused, you have to debug through to see where it goes. They're used exactly once, and they're only used as part of a long process. You've just increased the cognitive load of dealing with your product by a factor of 12. It's downright malignant.

Code should be split so that state is isolated, and business processes (intellectual property) is also self contained and testable. But don't buy into this "70 lines" rule. It makes no sense. 70 lines of python isn't the same as 70 lines of C, for starters. If code is sequential, and always running in that order and it reads like a long script; that's because it is!

Focus on separating pure code from stateful code, that's the key to large maintainable software! And choose composability over inheritance. These things weren't clear to me the first 10 years, but after 30 years, I've made those conclusions. I hope other old-timers can chime in on this.

The length of functions in terms of line count has absolutely nothing to do with "a more modular and maintainable codebase", as explained in the manifesto.

Just like "I committed 3,000 lines of code yesterday" has nothing to do with productivity. And a red car doesn't go faster.

“Ideally under 70 lines” is not “always under 70 lines under pain of death”.

It’s a guideline. There are exceptions. Most randomly-selected 100-line functions in the wild would probably benefit from being four 25-line functions. But many wouldn’t. Maturity is knowing when the guideline doesn’t apply. But if you find yourself constantly writing a lot of long functions, it’s a good signal something is off.

Sure, language matters. Domain matters too. Pick a number other than 70 if you’re using a verbose language like golang. Pick a number less if you’re using something more concise.

People need to stop freaking out over reasonable, well-intentioned guidelines as if they’re inviolable rules. 150 is way too many for almost all functions in mainstream languages. 20 would need to be violated way too often to be a useful rule of thumb.

Just chiming in here to say, absolutely you should keep functions small and doing one thing. Any junior reading this should go and read the pragmatic programmer.

Of course a function can be refactored in a wrongheaded way as you’ve suggested, but that’s true of any coding - there is taste.

The ideal of refactoring such a function you describe would be to make it more readable, not less. The whole point of modules is so you don’t have to hold in your head the detail they contain.

Long functions are in general a very bad idea. They don’t fit on a single screen, so to understand them you end up scrolling up and down. It’s hard to follow the state, because more things happen and there is more state as the function needs more parameters and intermediate variables. They’re far more likely to lead to complecting (see Rich Hickey) and intertwining different processes. Most importantly, for an inexperienced dev it increases the chance of a big ball of mud, eg a huge switch statement with inline code rather than a series of higher level abstractions that can be considered in isolation.

I don’t think years worked is an indicator of anything, but I’ve been coding for nearly 40 years FWIW.

> Say, you have a process that is single threaded and does a lot of stuff that has to happen step by step. > New dev comes in; and starts splitting everything it does in 12 functions, because, _a function, should do one thing

I would almost certainly split it up, not because "a function should only do one thing" but because invariably you get a run of several steps that can be chunked into one logical operation, and replacing those steps with the descriptive name reduces the cognitive load of reading and maintaining the original function.

And here's John Carmack on the subject of 1000s of lines of code in a single function: http://number-none.com/blow/blog/programming/2014/09/26/carm...

This is a balancing act between conflicting requirements. It is understandable that you don't want to jump back and forth between countless small subfunctions in order to meticulously trace a computation. But conceptually, the overall process still breaks down into subprocesses. Wouldn't it make sense to move these sub-processes into separate functions and name them accordingly? I have a colleague who has produced code blocks that are 6000 lines long. It is then almost impossible to get a quick overview of what the code actually does. So why not increase high-level readability by making the conceptual structure visible in this way?

A ReverseList function, for example, is useful not only because it can be used in many different places, but also because the same code would be more disruptive than helpful for understanding the overall process if it were inline. Of course, I understand that code does not always break down into such neat semantic building blocks.

> Focus on separating pure code from stateful code, that's the key to large maintainable software! And choose composability over inheritance.

100%!

I think that you are describing an ideal scenario that does not reflect what I see in reality. In the "enterprise applications" that I work on, long functions evolve poorly. Meaning, even if a long function follows the ideal of "single thread, step by step" when it's first written, when devs add new code, they will typically add their next 5 lintes to the same function because it's already there. Then after 5 years you have a monster.

Agree that "splitting for splittings' sake" (only to stay below an arbitrary line count) does indeed not make sense.

On the other hand I often see functions like you describe - something has to be executed step-by-step (and the functionality is only used there) - where I _whish_ it was split up into separate functions, so we could have meaningful tests for each step, not only for the "whole thing".

What would be a good example of the kinds of things a 100 line function would be doing?

I don't see that in my world so i'm naively trying to inline functions in codebases i'm familiar with and not really valuing the result i can dream up.

For one, my tests would be quite annoying, large and with too much setup for my taste. But i don't think i'd like to have to scroll a function, especially if i had to make changes to the start and end of the function in one commit.

I'm curious of the kinds of "long script" flavoured procedures, what are they doing typically?

I ask because some of the other stuff you mentioned i really strongly agree with like "Focus on separating pure code from stateful code" - this is such an under valued concept, and it's an absolute game changer for building robust software. Can i extract a pure function for this and separately have function to coordinate side effects - but that's incompatible with too long functions, those side effectfull functions would be so hard to test.

I have been programming professionally for 17 years and I think this guideline is fine. I have difficulty imagining a function of 70 lines that would not be better off being split into multiple functions. It is true that if a function is just a list of stuff longer functions can be allowed then when it does multiple different things but 70 lines is really pushing that.

Funny this is the assertion in the I would most agree to use as general design principle to apply as thoroughly as possible, with tightened variable scope on equal position. Though no general principle should be followed blindly of course.

That's not the the function length per se. A function that is 1000 lines of mere basic assignments or holding a single giant switch can sometime be an apt option with careful consideration of tradeoffs as origin of the design. Number of line doesn't tell much of the function complexity and cognitive load of will imply to grasp what it does, though it can be a first proxy metric.

But most of the time giant functions found in the wild grow up organically with 5 levels of intertwined control control moving down and up, accumulating variables instead of const without consideration to scope span. In that case every time a change is needed, the cognitive load to grasp everything that need to be considered to change this finding is extremely huge. All the more as this giant function most likely won't have an test suit companion, because good engineering practices are more followed at equal level on several points.

If you read Clean Code and other similar books, they don't necessarily advise moving the sub-functions to other files, or splitting them arbitrarily. They simply have the top function delegate to sub-functions that are lower in the same file. Even better if these sub-functions can be marked as private in your language (to avoid polluting the public API of your object). And here the goal is to use function names to document what each block of code (sub-function) does.

Example:

    def process_order(order):
        _validate(order)
        _reserve(order)
        _charge(order)
        _confirm(order)
    
    def _validate(order):
        ...
    
    def _reserve(order):
        ...

> They're used exactly once

To me, that's key here. That things are scattered over multiple files is a minor issue. Any competent IDE can more or less hide that and smoothen the experience. But if you have factored some code into a function, suddenly other places may call it. You have inadvertently created an API and any change you make needs to double check that other callers either don't exist or have their assumptions not suddenly violated. That's no issue if the code is right therr. No other users, and the API is the direct context of the lines of code right around it. (Yes you can limit visibility to other modules etc but that doesn't fully solve the issue of higher cognitive load.)

i see these rules and think “70 lines wow that’s short”

and then i read code and see a 50 line function and am like “wow this function is doing a lot”

sure strict rules aren’t amazing, but i think it would be cool to have a linter warning when there are more than X functions with over 70 lines (this is language dependent - verbosity)

I'm on the fence about this.

I see huge >130 line functions as a liability. There's so much state in it that a mistake on one line is not obvious. It makes those functions "sticky" and they tend to become the center of a lot of call graphs... like a neutron star. When a mistake is made maintaining or modifying this function it tends to have far-reaching side effects.

On the other hand some APIs (looking at you, OpenGL) are just so verbose that you can't avoid long functions.

I think it's generally good to compose functions from smaller functions where possible. Sometimes you can't and probably shouldn't. But it's hard to give a quantifiable rule in my experience. Approximations work but will never be perfect.

At first, I was thinking the same but then realized this is over a full page of code. It isn't an insane rule of thumb at all.

At least we aren't talking about "clean code" level of absurdity here: 5-20 lines with 0 - 2 parameters.

> Now you have 12 functions, scattered over multiple packages, [...]

Who says that the 12 functions need to be in multiple packages? And you can also keep them in the order you call them.

Having 12 functions is probably easier to test, too.

Yes, the 70 lines rules is arbitrary. But it's only as arbitrary as using 80 columns.

What has always baffled me is how CS uses the word "safety" where all other industries use "robustness".

A robust design is one that not only is correct, but also ensures the functionality even when boundary conditions deviate from the ideal. It's a mix of stability, predictability and fault tolerance. Probably "reliable" can be used as a synonym.

At the same time, in all industries except CS "safety" has a specific meaning of not causing injuries to the user.

In the design of a drill, for example, if the motor is guaranteed to spin at the intended rpm independently of orientation, temperature and state of charge of the battery, that's a robust design. You'll hear the word "safe" only if it has two triggers to ensure both hands are on the handles during operation.

Pretty good list, but a hidden assumption is that the reader works in an imperative style. For instance, recursion is the bread and butter of functional and logical programming and is just fine.

The most important advice one can give to programmers is to

  1. Know your problem domain.
  2. Think excessively deep about a conceptual model that captures the 
     relevant aspects of your problem domain.
  3. Be anal about naming your concepts. Thinking about naming oftentimes 
     feeds back to (1) and (2), forming a loop.
  4. Use a language and type system that is powerful enough to implement 
     previous points.

Zero technical debt certainly is... ambitious. Sure, if we knew _what_ to build the first time around this would be possible. From my experience, the majority of technical debt is sourced from product requirement changes coupled with tight deadlines. I think even the most ardent follower of Tiger Style is going to find this nigh impossible.

Lots of debating about the color to paint the fence in the design meetings for the nuclear reactor...

I don't know how this philosophy is applied at TigerBeetle. When I establish engineering guidelines I try to frame them as exactly that: guidelines. The purpose is to spawn defensible reasoning, and to trigger reflection.

For example, I might say this:

   We use a heuristic of 70 lines not as a hard limit, but as a "tripwire." If you cross it, you are not 'wrong,' but you are asked to pause and consider if you're introducing unintentional complexity. If you can justify it, keep it—there's no need to code golf.

"Style," "philosophy," "guides," they're all well-meaning and often well-informed, but you should be in command of the decision as the developer and not forget your own expertise around cohesion, cognitive load, or any functional necessities.

There are staunch believers in gating deploys based solely on LOCs, I'm sure... I like the idea of finding ways to transparently trigger cognitive provocations in order for everyone to steer towards better code without absolutes.

> Limit line lengths: Keep lines within a reasonable length (e.g., 100 characters) to ensure readability. This prevents horizontal scrolling and helps maintain an accessible code layout.

Do you not use word wrap? The downside of this rule is that vertical scrolling is increased (yes, it's easier, but with a wrap you can make that decision locally) and accessibility is reduced (and monitors are wide, not tall), which is especially an issue when such a style is applied to comments so you can't see all the code in a single screen due to multiple lines of comments in that long formal grammatically correct style

Similarly, > Limit function length: Keep functions concise, ideally under 70 lines.

> and move non-branching logic to helper functions.

Break accessibility of logic, instead of linearly reading what's going on you have to jump around (though popups could help a bit). While you can use block collapse to hide those helper blocks without losing their locality and then expand only one helper block.

Can you have a coding philosophy that ignores the time or cost taken to design and write code? Or a coding philosophy that doesn't factor in uncertainty and change?

If you're risking money and time, can you really justify this?

- 'writing code that works in all situations'

- 'commitment to zero technical debt'

- 'design for performance early'

As a whole, this is not just idealist, it's privileged.

The attribution to TigerBeetle should be at the top of the page with a link to the original tigerstyle, not buried at the bottom. Right now it reads like official TigerBeetle content until you scroll down, which isn't fair to either you or the original team.

I would not hire a monk of TigerStyle. We'd get nothing done! This amount of coding perfection is best for hobby projects without deadlines.

This just makes me want to write sloppy dangerous throwaway code with wild abandon

> Avoid recursion if possible to keep execution bounded and predictable, preventing stack overflows and uncontrolled resource use.

In languages with TCO (e.g. Haskell, Scheme, OCaml, etc.) the compiler can rewrite to a loop.

Some algorithms are conceptually recursive and even though you can rewrite them, the iterative version would be unreadable: backtracking solvers, parsing trees, quicksort partition & subprblems, divide-and-conquer, tree manipulation, compilers, etc.

I like the 100% philosophy for coding:

1. 100% code coverage 2. 100% branch coverage 3. 100% lint (without noqa) 4. 100% type check pass(for python/js) 5. 100% documentation coverage 6. All functions with complexity less than 5. All functions with no of lines less than 70. All files with number of lines less than 1000.

These make code high quality, and quality of life is directly proportional to qualify of your code.

The orginal piece is a much more nuanced read, I feel this one misses some context.

https://github.com/tigerbeetle/tigerbeetle/blob/main/docs/TI...

> Allocate all necessary memory during startup and avoid dynamic memory allocation after initialization.

Why?

Not to midwit but I will stick to MISRA C for this sort of thing. It is very clear in why each thing must be done and it is hard to argue against most of it. It’s usually where safety and robustness deeply matter and using it would have avoided a number of high-profile exploits we have seen in the recent past. While not every “rule” may be applicable to all languages, many standard languages could adopt a good number of rules from it and benefit greatly. Anyone with a number of years experience with some reflection on what is good, clear and unambiguous style would reinvent a decent portion of MISRA C.

I’ll let others speak to the Barr standard.

Interesting use of `latency_ms_max` as a naming convention. I'm definitely guilty of `max_latency_ms` instead, but they make a convincing argument for putting `max` at the end.

If this topic floats your boat, go look up the NASA coding standards. For a few projects, I tried to follow a lot of their flow control recommendations, and will still reach for: `while ... && LIMIT > 0` in some situations.

Still a huge fan of including some type info in the variable name, eg: duration_s, limit_ms makes it extremely clear that you shouldn't mix math on those integers.

"Zero technical debt" - I doubt this is feasible in practice.

> Do it right the first time: Take the time to design and implement solutions correctly from the start.

Doing good design is off course important, but on the other hand software design is a lot of times iterative because of unknown unknown s. Sometimes it can be better to create quick prototype(s) to see which direction is the best to actually "do it right", instead of spending effort designing something that in the end won't be build.

Just curious, is this something that evolved trying to tame agentic coding with rules ? because it does feel like something I will put in my CLAUDE.md

This advice is great but lacks context.

For many shops it’s too much effort for the payoff. Unless you work on medical devices or aerospace then maybe.

Your situation will warrant some of these things, or doing them to a lesser degree. Part of our role is to decide and recommend what’s appropriate.

> Allocate all necessary memory during startup and avoid dynamic memory allocation after initialization. Absolutely not an ultimatum advice, even harmful in most cases. Just measure you memory usage and don't rely on and avoid external OOM handler.

Master recursion and there will be nothing left to master. Avoid recursion and you will remain forever stuck in a loop.

This is the kind of development that one needs for safety critical applications. E.g., nuclear power plants or airplane control software. I don't think it is economically feasible for less critical software. It presumes a great degree of stability in requirements which is necessary for such applications.

a zero technical debt approach is good sometimes, but im not sure i would take it this far. It depends.