I can’t help but suspect it doesn’t offer much and you may as well just use match
statements for whenever you want pattern matching, however many times it might be slightly more verbose than what you could do with if let
.
I feel like I’d easily miss that pattern matching was happening with if let
but will always know with match
what’s happening and have an impression of what’s happening just from the structure of the code.
// Make optional of type Option<i32> let optional = Some(7); match optional { Some(i) => { println!("This is a really long string and `{:?}`", i); // ^ Needed 2 indentations just so we could destructure // `i` from the option. }, _ => {}, // ^ Required because `match` is exhaustive. Doesn't it seem // like wasted space? };
I think the rust book gives a good example. The match syntax is just a waste here.
So if you have a single expression that you want to match I think it is worth it.
As with most syntax, the more you read it the more you’ll just spot it without thinking.
I would say it’s very useful when you are looking for one specific pattern, which happens a lot with
Option<T>
. Plus, being able to chain it inif / else if / else
chains helps with organizing the code. It generally doesn’t grow as deep as withmatch
.That said,
match
is fantastic and it’s totally fine to prefer using it.if let
andlet else
are there for those cases when you tend to discard or not need to use the other values than the matched one. How often that happens depends on what you are doing.I’m not a massive fan of it – some Rust newbies on our team do get confused by it – but it can improve readability in places and it does fit into the greater scheme of Rust in that you can also write things like this:
struct Something(DifferentThing); let something = Something(DifferentThing::new()); let Something(different_thing) = something;
So, any time you see a
let
, it’s actually secretly pattern matching. The variable name you provide is just a wildcard pattern.EDIT: I copied this into a separate post: https://lemmy.ml/post/14593192
yea, great point … I hadn’t considered the consistency with destructuring (which seems silly in hindsight).
For those who aren’t aware, here’s the first section in The Book on patterns in
let
statements.I think, if this is confusing, there are two points of clarification:
- As Ephera states, all
let
statements involve patterns. They’re alllet PATTERN = EXPRESSION
. For ordinary variable binding, we’re just providing a basic pattern that is essentially like a wildcard in that it will match the totality of any expression and so be bound to the full/final value of the expression.- It’s only when the pattern becomes more complex that the pattern matching part becomes evident, as elements of the value/expression are destructured into the pattern.
- EG,
let (x, y, _) = (1, 2, 3);
or Ephera’s example abovelet Something(different_thing) = something;
which extracts the single field of thestruct
something into the variable
different_thing` (handy!).
let
statements must useirrefutable
patterns. That is, patterns that cannot fail to match the expression. For example, against a tuple,(x, y, _)
will always match. Another way of putting it, is thatirrefutable
patterns are about destructuring not testing or conditional logic.if let
statements on the other hand can take bothirrefutable
patterns andrefutable
, but are really intended to be used withrefutable
patterns as they’re intended for conditional logic where the pattern must be able to fail to match the expression/value.- See The Book chapter on
refutability
Excellent research! 🙂
- As Ephera states, all
If let sounds like swift to me which is used there in common practice.