Are we talking about this from the perspective of CS (algorithm optimization) or SE (code design)?
From an SE perspective, make a flatmap function that explicitly handles Collection<Optional<Walrus>>. The implementation doesn't matter. If your language/framework already has a compatible flatmap function, make a single frobnicate(Optional<Walrus>) function that returns whatever value is necessary for flatmap(frobnicate) to discard them.
From a CS perspective, doing a filter from Collection<Optional<Walrus>> to Collection<Walrus> is probably a bad idea. If your collection is small, nothing matters. If your collection is large, you probably don't want to spend time making a new copy of it. If your filter just returns a view rather than a hard copy, then there is no optimization benefit and you should just do whatever makes the most sense from an SE perspective. If frobnicate is cheap then you're paying the branch prediction failure tax anyway regardless of when you frobnicate, and if frobnicate is more expensive then your should probably parallelize and have each thread handle unpacking the Optional. Either way, you probably don't want to spend time making a copy.
These are all generalizations based on hypotheticals and there are certainly a lot of exceptions, but broadly speaking I don't see a strong argument here. If optimization matters then optimize based on your own profiling of your situation, and if optimization doesn't matter then design your functions based on what features and paradigms are available/common in your area.
I am continually impressed by the ability of LLMs to take trivial ideas and turn them into lengthy and obtuse blog posts with unnecessary analogies.
Debasish has been writing for a long time. I have one of his books on FP in my office.
Honestly, this just looks like one of those lingo-heavy-but-surface-level blog posts that used to make functional programming spaces so insufferable to everyone on the outside
You want to avoid branches in hot paths. If you branch inside the loop, lots of branches. If you branch outside the loop (into different specialized loops), few branches. Big fucking deal.
bool w;
int x[1000];
int y[1000];
for(int i=0;i<1000;i++){
x[i] += y[i];
}
if(w){
for(int i=0;i<1000;i++){
y[i] = 0;
}
}
Slower but prettier with the
if pushed down.
Is that true? The loop is a branch.
Who actually considers a loop a branch? A loop is a chunk of code that will be run N times depending on some evaluation that’s run before or after an iteration. A branch is a single decision which of several pieces of code to run, once.
>Who actually considers a loop a branch?
The machine?
The "go around" branch is obviously not completely avoidable (though unrolling helps). Branches inside the loop body sometimes are.
These things are so divorced from the reality of programming, even when they involve actual code instead of fancy lingo. Like in Scala, not a pure functional language, tutorials used to find the most convoluted higher-order functional way to do simple things.
And also generate a shorter version.
Semantic compressor and decompressor
Yet another encroachment on traditionally human activity.
I know we’re not supposed to comment just for that, but this might be my single favorite joke comment I’ve ever read here. Good job.
Except that TFA is a bog standard example of traditional human activity and the GP's comment is nonsensical trolling.
I'm continually impressed by the ability of humans to spam low-effort whining about suspected LLM writing in almost every HN thread.
It's an LLM-generated article.
How do you know? Doesn't read particularly LLM written to me, and even if it is, it's quite well written.
The author has been blogging about this kind of stuff for over 20 years. I'd be surprised if they suddenly let bots autonomously spam their blog.
Yeah, sounds human-written to me, too. Out of habit I checked with Pangram - which identifies some parts as AI-written. (I think that might be false positives but am not 100% sure.)
This particular blog post didn't really stand out to me as having a lot of Claudeisms, though there were some parts of it that definitely made me raise my eyebrow. Just little things here and there, and also near the end where the words "pay" and "cost" stand out a lot in the particular ways they were used.
I was curious if this was just my own stupidity, just human pattern matching run amok. So I decided I'd go back a bit and check another article to see if it felt like that. My initial plan was to go far back enough to when AI usage would've been less likely, but as far as I can tell this particular blog only goes back this far, from april of this year:
https://debasishg.github.io/blog/pin-dyn/
Ah, there's our friend Claude. I dunno if I got lucky and picked literally the only article with "load-bearing", but I promise, it wasn't my intention.
This newest article is a lot less egregious in terms of LLM-isms, but I can see why it triggers the AI spidey senses too. If I had to guess I'd be more conservative and guess it was AI-assisted rather than AI-generated, although I'm sure some people have some skills or tools that can do a relatively good job weeding out the more overt LLMisms and even give Pangram a bit of trouble.
Of course in reality, given how many full complete blog posts with things like diagrams they have since April of this year, I think it's only reasonable to say that it would be a little on the surprising end if they weren't using LLM assistance.
It's sad that it's come to this, though. Some days it feels like I'm in a weird low-stakes version of The Thing.
I've always believed the opposite: get conditionals deep in your code so that the higher level control flow is regular.
But I suppose my greater philosophy for making code that avoids bugs is that you have a couple things that are done when dealing with data:
- distribution
- deciding
And you want to avoid distribution and deciding being mixed together in the same spot.
"Distribution" can be for loops but also breaking up some data based on some key into N bistinct buckets
"Deciding" is where you're looking at the data more closely to make some decision (like "is this a big customer or a small customer")
Distribution often involves decision making, but if you mix them all in one spot you can obfuscate your decision points. Splitting it up just makes things "obviously" right or "obviously" wrong. Perf stuff is another discussion of course, but in practice most things are not at a scale where it matters.
by_category = defaultdict(list)
for d in data:
by_category[category(d)].append(d)
for category, per_category_data in by_category.items():
do_thing(category, per_category_data)
I really value code patterns that make mistakes obvious, or at least makes it harder to stuff a mistake in somewhere. Some patterns are harder to describe in this model though.
(I do like the advice of having a consistent vocabulary for working on collections as a principle though, I just find that top-level conditional use tends to quickly get you into "... why is this method not called" territory, which is a more annoying problem than "why is this slow")
That's another good way to look at it - sometimes the "base" is more like a physics substrate. Physics doesn't care about semantics, it just is. Putting semantics first would be weird.
I guess it's a case of perspective
I think compilers can push out ifs inside for to be one if with two fors.
I've done this for years. Not every time of course but where it makes the code easier to understand and maintain.
Speed was almost never the reason.
I take it you never rewrote a Matlab for loop as a vector/matrix op for insane speedups then :)
Erm, no? You write f(w: Walrus) -> Walrus and then let the caller handle Walrus|None and Iterable[Walrus] however they wish!
And if someone decides the codebase needs an abstraction over (and therefore specific functions to handle) Iterable[Walrus|None] then you check the weather and suggest they take a break and go for a stroll. (You check the weather to see if you should lend them your brolly.)
What am I missing?
What is missing here is any benchmarks backing up this argument for code structure.
Of note, as of C#9 (and maybe prior), the dotnet runtime does this automatically whenever it is deemed safe. https://devblogs.microsoft.com/dotnet/performance-improvemen...
The same technique is applied as an optimization, when deemed safe, in all current gen c compilers (gcc, llvm, etc).
I'm very confused why neither measurements nor references to when this is done automatically in most modern languages is included in the article.
At least in JVM land, it's pretty easy to thwart that optimization. Particularly if the condition is on a mutable yet unchanged in the loop value.
For example:
var map = new HashMap<String, String>();
map.put("foo", "bar");
for (var i : items) {
if ("bar".equals(map.get("foo")) {
doStuff(i);
}
}
Even though `map` isn't mutated, it's hard enough for the JVM to detect and the underlying `get` functions are complex enough that it'll run the `get("foo")` every time, which can be quite expensive.
Can't speak for C# but in C/C++ the optimization can rarely be applied safely due to aliasing. If any part of the data you're working with involves a char* then C/C++ optimizers refrain from doing these kinds of optimizations because of how difficult it is to guarantee the absence of mutability.
Didn’t see it mentioned in the article but isn’t leading with if-statement called a “guard clause”.
I like that pattern but it’s just general best practice I thought.
Guard clauses are things that return early for trivial or problematic cases. Like https://en.wikipedia.org/wiki/Guard_(computer_science)#Flatt...
They're one of those good practices that look like bad practice to everyone who just got a CS degree. Seems ex-students are unsettled by asymmetry or want to minimize the number of return statements.
Oh, guard clauses might also use continue statements in loops
Why am I even in this function if it shouldn't happen?
Because a lot of languages can't easily express the semantics of "you're not allowed to call the function this way". I mean, suppose you have a function that takes two integers, but the second must be greater than the first. Most type systems don't have any way to represent that at all, let alone conveniently.
Related: don't write if(arg == null) throw ArgumentNullError; at the top of every function. If it's not supposed to happen then just let it throw the error naturally when you dereference it. In C it's even worse because you turned an easily caught segfault into a silent nop.
If the criteria for it not happening is too complicated to expose to the caller
Particularly for high performance code when branch prediction is taken to account
Is the idea that "accidental casework" should be moved up, whereas the "reusable bulk ontology" should be moved down?
There's very high-leverage abstractions that completely constrain a space. An example is a good definition - you can't think of something outside to compare it to, it just is. These things survive for a long time since they define it.
But if you're trying to do that philosophy super deep into a program, you're probably violating a bunch of invariants subtly.
Of course, there is no good separation at the end of the day as we all know from spaghetti codebases :)
I have always phrased this as "Never do one of something".
Just the branch predictor gains are probably worth it.
this is just a guard on the function definition?
I like it, but to do fizzbuzz in this way, you'd have to separate what's inside the loop into a reused function.
I think it's sort of obvious that the limit to this general rule is when data dependencies between fors and ifs forbid you from pushing things further up/down.
TL;DR in one sentence:
"the loop runs without a branch, and is a candidate for vectorization".
That's it, that's the article. This matters a lot in huge-scale / scientific computing / HPF, where if you can express something as an operation on vectors on matrices, you win big (those ops parallelize well, can be run on GPUs, clusters, what have you).
For the 99% of developers who are shuffling data around constrained by I/O, you win small.