There are no C style "for" loops in Rust: https://doc.rust-lang.org/reference/expressions/loop-expr.ht...
There is the "for" expression, but that does not give you a C-style "for" loop. It gives you something akin to a "foreach" you might see in Java, C#, Go, etc.
It's especially odd to point out this language detail, because for expressions always return the unit type. So it's not like you can do something with the return value (unlike loop expression, which can evaluate to one of its break expressions).
It’s the reason for crates like itertools.
I don’t think that is pedantic at all.
The author was contrasting loops - an imperative construct (which both C-style for and iterator-based for are examples of) - to the functional style of chaining iterator functions, adapters & reductions and passing closures around.
FWIW I agree with you, it's just that I was trying to make a distinction between imperative and functional style in Rust (just like the author was trying to do) - not literally claiming Rust has C-style for loops.
> A for expression extracts values from an iterator, looping until the iterator is empty.
They look like this:
for i in 1..10 {
println!("{i}");
}
EDIT: Okay you edited your comment to say this doesn't count. Sure. This is what the author of the post was talking about, though.
>>That's not really the case. For loops are certainly less common compared to C, but they are completely fine to use. Forcing every loop into an iterator-chain style can quickly become an unreadable mess.
Implies a C-style for loop, some sort of counting accumulator, and an update expression. That doesn't exist in rust. That's all I was saying.
I know who you are, so I know I'm preaching to the preacher.
> For loops are not idiomatic in Rust - writing Fortran-ey code instead of iterators will lead to pain and slower loops. Spending time reading the examples in the iterator docs and the community solutions in the exercisms will help a lot.
I think they are talking about C style for loops or Fortran style do loops, they explicitly contrast against iterators.
Edit: Although, I wonder, what does an iterator like you’ve shown compile down to? I’d imagine Rust is smart/modern enough and that iterator is common enough that the assembly emitted looks a lot like a c for loop. Or better.
(0..10).iter().for_each(|x| println!("{x}"))
Many folks do not think of Rust's for loops as using iterators under the hood, and so will often talk about them as though they don't use iterators, even though they technically do.
When I wrote this, my main takeaways were numerical computations with arrays, which don't tend to use for loops in Rust, and which require grokking iterators for maximum performance and rayon-parallelism boons.
To a Julia audience, seeing this style of iterator chaining is quite a new flavor to think about composing computation, so I wanted it was with that audience in mind that I wrote this.
Yeah I think that makes sense! I don't do that kind of work and so it's more usual in the kinds of code I write.
Since the .next() implementation of std::ops::Range is essentially an i++, you'll quickly arrive at a similar representation as classic C for-loop.
All the other syntax, including both "for" and "while" loops and the related but technically different "while let" loop, while useful to humans to communicate intent, aren't semantically different - and so they're transformed early in compilation, they are just "syntax sugar" and are de-sugared into rather elaborate loops with their exit condition now a loop break condition etc.
But yes, as in C++ and similar languages, the iterators generate the same machine code as you'd have gotten for writing the C-style for loop from the 1970s, it's just that in Rust you literally can't write that loop.
Hypothetically if you do
for i in 1..10 {
println!("{i}");
}
{
let result = match IntoIterator::into_iter(1..10) {
mut iter => loop {
let next;
match iter.next() {
Some(val) => next = val,
None => break,
};
let i = next;
let () = { println!("{i}"); };
},
};
result
}
And so in some sense, "loop" is more primitive than "for".
> But then hypothetically the assembly output could… end up not even having a loop at all
Absolutely, with any of these loops, the compiler may not emit a loop in assembly. And in this case, that seems to be true: https://godbolt.org/z/7Gq69Gvre
for i in range(10):
print(i)