Weird Expressions in Rust

https://www.wakunguma.com/blog/rust-weird-expr

by lukastyrychtr • 1 year ago

195 151 1 year ago

wakunguma.com

xyst• 1 year ago

These “weird expressions” probably get used code golf.

steveklabnik19• 1 year ago

Basically none of them are actually useful, or even do anything, it's mostly a parser stress test.

behnamoh• 1 year ago

Great, now this stuff gets fed into LLM trainings and we'll see them in the next-gen model outputs.

Seriously though, I love "abusing" programming languages in unexpected ways. My favorite so far is: https://evuez.net/posts/cursed-elixir.html. Reading this made me realize Elixir is literally macros all the way down, and it's a Lisp!

ramon156• 1 year ago

Note that for Rust devs these are also weird syntaxes. I feel like some people assume that an experienced dev can read these, but it takes a while to get what's going on.

ChuckMcM• 1 year ago

Kind of like obfuscated C code I suspect.

dathinab5• 1 year ago

yes, but less risky (and less power full) because you often very fast can conclude that "whatever it does it's safe, sound and doesn't affect unrelated code"

01HNNWZ0MV43FF• 1 year ago

Yeah. I've been doing Rust for a few years and when I look at these I just see "Failed PR review, unreadable to humans"

b0a04gl• 1 year ago

they exist because whole language built to treat expressions as firstclass citizens : blocks, ifs, matches, even macros as expressions that return values. so once you internalize that, all these weirdo one liners are artifacts. just artifact of a system where expressions compose infinitely. the syntax tree runs deeper than most people's habbits allow. you hit that depth and brain says this is wrong but compiler's allowing.

gmueckl4• 1 year ago

If a language that claims to be security focused is easily able to express constructs that human minds find barely comprehensible, or worse, then this is itself arguably a security issue: it's impossible to check the correctness of logic that is incomprehensible.

PaulHoule• 1 year ago

It is a critique of macros. 500 lines of Common Lisp replaces 50,000 lines of C++ but those 500 lines make no sense at all the first time you see them.

steveklabnik19• 1 year ago

If a language that claims to be security focused

Rust does not claim to be particularly security-focused, only memory safe.

Also, this means that you'd consider any expression-based language to be inherently a security problem.

pornel4• 1 year ago

What's the threat model? If you're reviewing untrusted or security-critical code and it's incomprehensible, for any reason, then it's a reject.

Syntax alone can't stop sufficiently determined fools. Lisp has famously simple syntax, but can easily be written in an incomprehensible way. Assembly languages have very restrictive syntax, but that doesn't make them easy to comprehend.

Rust already has a pretty strong type system and tons of lints that stop more bad programs than many other languages.

int_19h6• 1 year ago

"never" is an easily comprehensible concept once you start asking the right questions.

But also, all examples in TFA are very artificial convoluted code. Meaning that you can write things like these just like you can write something like &&&...x - but why would you? Actual real-world uses of this feature are all quite readable.

derriz5• 1 year ago

That sounds superficially reasonable to me and I'm all for regularity in programming language semantics but on thinking about it further, I actually think it's a design flaw.

It makes no more sense to me for "return <expr>" to have a type than it does to make "if <expr>" or "break" or "{" or any other keyword to have a type. These are syntactic elements.

Rust's type system is clearly inspired by Hindley-Milner and most languages using such a type system either don't even have a return keyword.

Even if you disagree with this argument, this design decision has resulted in all these weird/confusing but absolutely useless code examples and there is no upside that I can see to this decision in terms of language ergonomics. What practical value is it to users to allow "return <expr>" to itself be an expression? That you can use such an "expression" as arguments to function calls with hilarious wtf consequences? It's a piece of syntactic sugar.

steveklabnik19• 1 year ago

Respectfully, "it makes no sense to me" isn't an argument. if and break both have types in Rust as well.

don't even have a return keyword.

This is because they are not procedural languages, it has nothing to do with the type system.

there is no upside that I can see to this decision in terms of language ergonomics.

There's tremendous upside! That's why lots of languages choose this. For example, there is no need for the ternary in Rust: if can just do that.

What practical value is it to users to allow "return <expr>" to itself be an expression?

Code like this just works:

        let guess: u32 = match guess.trim().parse() {
            Ok(num) => num,
            Err(_) => return,
        };

That is, if return wasn't an expression, we'd have a type error: the two arms would have incompatible types.

NobodyNada2• 1 year ago

In practice, it's quite a useful feature, because you can write things like this:

    let day_number = match name {
        "Sunday" => 0,
        "Monday" => 1,
        "Tuesday" => 2,
        "Wednesday" => 3,
        "Thursday" => 4,
        "Friday" => 5,
        "Saturday" => 6,
        _ => return Err("invalid day")
    };

bobbylarrybobby2• 1 year ago

The issue with `return expr` not having a type is that you lose the ability to write something like

let y = match option { Some(x) => x, None => return Err("whoops!"), };

Without a type, the None branch loses the ability to unify with the Some branch. Now you could say that Rust should just only require branches’ types to unify when all of them have a type, but the ! never type accomplishes that goal just fine.

deathanatos• 1 year ago

We can use match to do pattern matching:

  let name = match color_code {
    0 => "red",
    1 => "blue",
    2 => "green",
    _ => "unknown",
  };

The RHS of the `=>` has to be an expression, since we're assigning it to a variable. Here, you should already see one "useful" side-effect of what you're calling "syntactic elements" (I'd perhaps call them "block statements", which I think is closer to the spirit of what you're saying.) The whole `match … {}` in the example above here is an expression (we assign the evaluation of it to a variable).

What practical value is it to users to allow "return <expr>" to itself be an expression?

Now, what if I need to return an error?

  let name = match color_code {
    0 => "red",
    1 => "blue",
    2 => "green",
    _ => return Err("unknown color"),
  };

The expression arms need to be the same type (or what is the type of `name`?). So now the type of the last branch is !. (Which as you hopefully learned from TFA, coerces to any type, here, to &str.)

There's more ways this "block statements are actually expressions" is useful. The need not be a ternary operator / keyword (like C, C++, Python, JS, etc.):

  let x = if cond { a } else { b };

In fact, if you're familiar with JavaScript, there I want this pattern, but it is not to be had:

  const x;  // but x's value will depend on a computation:
  // This is illegal.
  if(foo) {
    x = 3;
  } else {
    x = 4;
  }
  // It's doable, but ugly:
  const x = (function() { if(foo) { return 3; } else { return 4; }})();
  // (Yes, you can do this example with a ternary.
  // Imagine the if branches are a bit more complicated than a ternary,
  // e.g., like 2 statements.)

Similarly, loops can return a value, and that's a useful pattern sometimes:

  let x = loop {
    // e.g., find a value in a datastructure. Compute something. Etc.
    if all_done {
      break result;
    }
  };

And blocks:

  let x = {
    // compute x; intermediate variables are properly scoped
    // & cleaned up at block close.
    //
    // There's also a slight visual benefit of "here we compute x" is
    // pretty clearly denoted.
  };

> Even if you disagree with this argument, this design decision has resulted in all these weird/confusing but absolutely useless code examples

I think one can cook up weird code examples in any language.

dathinab5• 1 year ago

it doesn't need to make sense on a higher abstraction level of logic/semantics

I mean you don't see any of the nonsense in the blog post in any realistic PR (so they don't matter),

but you would run into subtle edge case issues if some expressions where more special then other expressions (so that does matter),

especially in context of macros/proc macros or partial "in-progress" code changes (which is also why `use` allows some "strange" {-brace usage or why a lot of things allow optional trailing `,` all of that makes auto code gen simpler).

pornel4• 1 year ago

This makes the language more uniform. Instead of having a special ternary ?: operator for if-else in expression position, you have one syntax everywhere.

It makes generic code work without need to add exceptions for "syntactic elements". You can have methods like `map(callback)` that take a generic `fn() -> T` and pass through `T`. This can work uniformly for functions that do return values as well as for functions that just have `return;`. Having nothingness as a real type makes it just work using one set of rules for types, rather than having rules for real types plus exceptions for "syntactic elements".

throwawaymaths• 1 year ago

its not just that some things you would usually think are control flow are expressions, its also that there are unusual rules around coercing the `noreturn` type.

tialaramex3• 1 year ago

The only "unusual" rule here is that Rust offers the zero type addition, but does not provide the (much more complicated) other type additions

So Rust does have: String + ! = String

But Rust doesn't have: String + i32 = Either<String,i32>

Note that the never type ! isn't special here, Rust will also cheerfully: String + Infallible = String or if you were to define your own empty type like so:

    enum MyEmptyType {} // MyEmptyType has no possible values

Now under type arithmetic String + MyEmptyType = String and indeed that works in Rust.

Edited: Syntax fix

AIPedant2• 1 year ago

Hmm my read is this is a slight overstatement - Rust was always built with the idea of expressions as first class citizens, but practicality and performance requires expression-breaking keywords like “return” which don’t fit neatly in an ML-ish language and have a few plain old hacks associated with implementing them (not “hack” as in lacking robustness; I mean theoretically/formally inelegant). Likewise there’s some stuff (u8) which is a simple syntax quirk. But a lot of these return/etc oddities are because Rust is ultimately an imperative language with strong influence from functional programming.

steveklabnik19• 1 year ago

return is an expression in Rust, and it fits in well.

There are very few statements: https://doc.rust-lang.org/stable/reference/statements.html

and a lot of expressions: https://doc.rust-lang.org/stable/reference/expressions.html

efnx2• 1 year ago

I’ve found rust to be an ML in C’s clothing.

The main difference from other MLs is the lack of higher kinded types, so it’s difficult to express things like Functor, Monad, Arrow, etc

GrantMoyer• 1 year ago

Haskell has `bottom`[1] (see also [2]), which acts like Rust's `return` from a type checking perspective.

I wouldn't call using a uninhabited type for the type of a return expression theoretically inelegant. On the contrary, I find it quite pleasing.

[1] https://wiki.haskell.org/Bottom

[2] https://en.wikipedia.org/wiki/Bottom_type

saghm5• 1 year ago

I'm confused about your parenthetical about "u8". What does the name of the unsigned 8-bit integer type have to do with whether the language is imperative?

nine_k2• 1 year ago

This is logically sound, but pragmatically not so. I wish the compiler could issue a warning or even an error if an expression of type `never` is used in a logical condition, like that of an `if`. While such cases might have rare legitimate uses (e.g. some edge cases of macro expansion, etc), I'd like it to be marked explicitly, similar to `unsafe`, e.g. with some `allow_never_as_condition` marker.

Likely the same should apply to expressions of type `()`.

steveklabnik19• 1 year ago

This post is missing my favorite one!

    fn evil_lincoln() { let _evil = println!("lincoln"); }

What's weird about this?

To understand what evil_lincoln is doing, you have to understand very old Rust. Here's the commit that introduced it: https://github.com/rust-lang/rust/commit/664b0ad3fcead4fe4d2...

    fn evil_lincoln() {
        let evil <- log "lincoln";
    }

log was a keyword to print stuff to the screen. Hence the joke, https://en.wikipedia.org/wiki/Lincoln_Logs Now that log is the println! macro, the joke is lost.

It doesn't say explicitly why this is "weird", but given some other comments in the file,

    // FIXME: Doesn't compile
    //let _x = log true == (ret 0);

I am assuming that using the return value of log was buggy, and so this tested that you could save it in a variable. I don't remember the exact semantics of log, but if it's like println!, it returns (), which is useless, so binding it to a variable is something you'd never write in real code, so it's "weird" in that sense.

ibotty• 1 year ago

What's the joke exactly? English is not my native language.

jerf• 1 year ago

https://www.basicfun.com/lincoln-logs/

This would be something the Boomer generation grew up with, and I think maybe the previous generation too. They're still around but they've certainly faded; they used to be Lego-level popular kids toys back then. They are named after President Lincoln, but only as a marketing tactic to use some of his reputation, there's no real connection.

I would imagine even some native English speakers are learning something with this post. I haven't seen them in a while.

rendaw• 1 year ago

What's the joke exactly? English is my native language.

steveklabnik19• 1 year ago

log "lincoln" is a reference to the toy "lincoln logs"

mbStavola• 1 year ago

A dog entered a tavern and said: "I cannot see anything, I'll open this one!"

hansjorg• 1 year ago

Tough crowd.

san1927• 1 year ago

love this one thats a really underrrated fact

nikolayasdf1232• 1 year ago

this is why I like Go

timeon• 1 year ago

It does not have stress tests for parser?

nemo16182• 1 year ago

I wonder, what's the "weirdest" expression in Go? Here's one:

   type Foo struct{}
   func (Foo) Bar() { println("weird...") }
   func main() {
    ([...]func(){^^len(`
   
   
   `): (&Foo{}).Bar})[cap(append([]any(nil),1,2,3))]()
   }

assbuttbuttass2• 1 year ago

Makes sense to me, [...]func() is an array of functions, and [...]T{index: value} is uncommon but still perfectly comprehensible

nikolayasdf1232• 1 year ago

this the worst? not too bad. fairly comprehensible.

yencabulator• 1 year ago

I have a personal fondness for silly variations of

  type __ *[]*__

techbrovanguard• 1 year ago

this is not the gotcha you think it is, you just dropped your gluestick

IshKebab2• 1 year ago

Honestly I'm surprised how not weird these are. Way less WTFy than Javascript, PHP, C or C++.

dathinab5• 1 year ago

yes but to be fair the blog is focused on unusual aspects of everything being an expression

you still can create some more confusing things by idk. overloading some operators (but luckily not `=` and similar crazy C++ things) adding recursive macros and maybe combining it with lifetime variance and coercion edge cases, maybe sprinkle in some arcane `#[]` annotations and people with be very confused, more so then in the article

IshKebab2• 1 year ago

Yeah... I'm just saying I haven't seen anything close to these things:

https://github.com/denysdovhan/wtfjs

https://github.com/satwikkansal/wtfpython

Thaxll• 1 year ago

Why assigning a variable to a function that returns nothing is not a compilation error?

steveklabnik19• 1 year ago

Which example are you referencing?

assbuttbuttass2• 1 year ago

There's no such thing as a "function that returns nothing" in Rust. Unit, written as (), is a first class value and can be assigned to a variable, although there's not much point

tialaramex3• 1 year ago

Do you mean a function which returns "nothing" in the sense that it does return but it has no particular value to return, like Vec::clear which gets rid of the values but preserves the capacity of the container ?

In Rust the return type of this function is the unit type, the empty tuple (). So, the variable has this type, there's no problem with this in Rust, even though some lesser languages can't handle the idea of a type this small.

Or did you mean a function which never returns, like std::process::exit ? In Rust this function's return type is ! the Never type, an empty type that you ordinarily can't name in stable Rust.

Because this type is empty, a variable of this type will evaporate, the compiler knows that we can't bring values into existence if there are no values of that type, the code paths in which this variable exists will never be executed, so no need to emit machine code.

In a language with generic programming like Rust this isn't an error, it's actually a convenience. We can write generic error handling code, and then for cases where there will never be an error our error handling code doesn't even compile, it evaporates entirely, yet for cases which can have actual errors, the error handling code is emitted.

dathinab5• 1 year ago

assuming you mean returning () (the empty tuple/void type)

because it doesn't compose well with generics, macros, proc-macros etc.

e.g. if you have this dump way to wrap clone: `fn foo<T: Clone>(v: T) -> (T, T) { let new = v.clone(); (v, new) }` it would implicitly not work with T = (), because then `v.clone()` would be a "function which returns nothing".

In isolation this might seem fine but if you compose abstractions you sooner or later run into an edge case where it isn't fine.

And this becomes even more a problem when macros/proc-macros are involved.

It also makes changing code easier, lets say you have something like `let x = foo(); dbg!(x);` and you change the return type it will keep compiling as long as the type implements `Debug`, even if you change the type to `()` (i.e. return nothing). And again for normal code that is a minor nit pick, but for macros, proc macros, generic code of sufficient complexity sooner or later you run into edge cases where it really matters that it's allowed. Not often but often enough.

Lastly and most importantly assigning `()` to a variable hurts no one, you won't see any such code in normal PRs.

So it it doesn't hurt anyone but can be quite use full in edge cases.

Lastly linters (mainly clippy) do warn or error for some of this nonsensical things, depending on the lint-set you enabled.

npalli• 1 year ago

yeah this is good, but now add lifetime annotations to have fun.

steveklabnik19• 1 year ago

Lifetimes are not expressions and therefore can't really be put into odd places.

armchairhacker• 1 year ago

Rust programs that give unintuitive outputs or compile errors.

Sniffnoy2• 1 year ago

I don't understand the one with dont(). Why does i.get() end up false at the end? Shouldn't it be true after having been set by dont()?

LegionMammal978• 1 year ago

The final line "assert!(i.get());" asserts that i.get() is true in the end. The ! character here belongs to the assert! macro, not a boolean negation. (This unfortunately gets a bit weird-looking when you want to write sensible stuff like "if !matches!(x, Some(5..=10)) { ... }".)

Sniffnoy2• 1 year ago

Oops, I see, thanks!

arjvik• 1 year ago

I figured out how return-as-a-value made sense only upon realizing that in the following code,

    fn funny(){
        fn f(_x: ()){}
        f(return);
    }

f() is never called because funny() returns before it gets called.

The reason you want return to be coercible to any type is so that you can write something like

    let x: i32 = if y {
        4
    } else {
        return; // type ! coerced into i32
    }

And you pick the return value of ! because return never actually produces a value that is propagated on at runtime, it immediately exits the function.

(Note this all works even with returning a value)

kzrdude2• 1 year ago

Many of them are on the same theme - the theme is `return -> !`.

Here's my favourite on that theme, which I was missing from the list:

    return return return return return return return return return 1

wredcoll3• 1 year ago

Is there some meanining to the number of returns?

kzrdude2• 1 year ago

No, it's just nonsense. Same result with fewer or more returns..

pluto_modadic• 1 year ago

I've absolutely seen some /cursed/ rust one liners.

if you extend it to the most cursed ~6 lines of code, you really can obfuscate what you're doing in a way that's fiendishly hard to debug.

munificent2• 1 year ago

Does anyone know why `union` isn't a reserved word in Rust?

Most contextual keywords in other languages come from either:

1. Features that were added after the language was in wide use and can't add keywords without breaking existing code.

2. Features where the word is particularly useful elsewhere, so would be painful to reserve (like `get` and `set` in Dart).

But neither of those seem to apply to Rust. As far as I know, it's always had ML-style unions, and "union" doesn't seem to be a particularly useful identifier otherwise.

Why isn't `union` fully reserved?

steveklabnik19• 1 year ago

It's simply that Rust has higher standards for breaking changes than "probably not in wide use." In other words, that someone could have had `let union =`... somewhere was a reason to make it contextual.

https://rust-lang.github.io/rfcs/1444-union.html#contextual-...

munificent2• 1 year ago

Ooooooh, I see my confusion now.

My brain switched off and I got enums and unions confused. I was like, wait, hasn't Rust had them since day one? I was thinking of `enum`, not `union`. My bad.

pitaj• 1 year ago

It's a common operation on sets, so would make `HashSet::union` [1] and friends less obvious, for no real benefit.

[1] https://doc.rust-lang.org/stable/std/collections/struct.Hash...

JoeOfTexas• 1 year ago

Bruh, I started learning Rust yesterday. Why do you do this to me. Now I don't know anything I studied.

steveklabnik19• 1 year ago

You don't need to know any of this. It's just a parsing stress test, with meaningless programs. It's fun trivia.

xg15• 1 year ago

Rust noob here.

That '!' type seemed weird in the first few examples but starts to make sense later on.

It's essentially a "pseudo type" for everything that is syntactically an expression, but will never return anything, because evaluating it causes the entire statement to be canceled.

Is that correct?

Analemma_2• 1 year ago

Yes. If you look at steveklabnik's example with the match statement elsewhere in the comments, it makes sense that '!' is the "never" or "unreachable" type, not because the return expression isn't run, but because its value will never be assigned to a variable, since it causes an unconditional exit from the function.

NobodyNada2• 1 year ago

Yes, exactly -- it's called the Never type.

It's also useful in more places than return expressions -- for example, you can make a function return ! to indicate that it's a non-returning function, which is useful for expressing, say, an error handler that must crash the program; or a main loop that must never return. It also can help the compiler generate more compact code when a function is known to not return.

There's currently work in progress to allow you to specify ! as a type everywhere, not just as function returns. This is useful where some generic code expects a function to return a Result with an implementation-specified error type, since an infallible implementation can specify ! as the error type. Then, the type checker can allow the programmer to unwrap a Result<T, !> without checking for errors, and the optimizer can remove the error-checking branches from generic code: https://doc.rust-lang.org/std/primitive.never.html

This has taken a very long time to implement, because of some very subtle implications on type inference that made it difficult to stabilize without breaking compatibility -- but the 2024 edition finally figured out a way to make it possible.

int_19h6• 1 year ago

Not necessarily the entire statement, just some outer expression.

Which might make more sense when you remember that the only statements in Rust are various declarations (`let`, `type`, `fn` etc) and macro invocations. Everything else is an "expression statement", including blocks and loops. Thus you can do stuff like:

    // Compute the first Fibbonaci number >10
    let n = {
        let mut x1 = 0;
        let mut x2 = 1;
        loop {
            let x = x1 + x2;
            if x > 10 { break x }
            x1 = x2;
            x2 = x;
        }
    };

Note that `break` never leaves the let-statement here - it just terminates the loop expression and forces it to yield a value (`break` without arguments yields (), and ditto for loops without break).

You can also break out of regular blocks if they are labelled and you use the labelled form of break:

   let x = 'label: { ... break 'label 42 ... }

This all can very easily lead to convoluted code if not used sparingly, but sometimes a mutating loop with mutable data encapsulated within and a break to yield it once the computation is complete is genuinely the most straightforward way to write something.

lacker• 1 year ago

I think there's a mistake in the explanation for "bathroom_stall". When describing the guard in this expression:

  if (i+=1) != (i+=1)

The post says, "The if statement is always going to be false because the right expression will always be one more than the left." But it's a not-equals. The if statement is always going to be false because in Rust "i += 1" doesn't return an integer value, it returns a (). So comparing any two += statements, they are always equal. Since the guard is a != comparison, the if statement is always false.

keybored2• 1 year ago

Once I tried how many `{{{...}}}` I needed to make javac crash. It wasn’t that many.

sureglymop• 1 year ago

With yesterdays release let chains got released. Really needed feature but can sometimes look pretty cursed: https://blog.rust-lang.org/2025/06/26/Rust-1.88.0/#let-chain...

bensons1• 1 year ago

I am sort of amused, a memory safe language deploys this sort of juggling

nfrmatk• 1 year ago

There's a fun RustConf talk on this topic from a few years ago. https://youtu.be/tNVDjMxCz-c

matt_kantor• 1 year ago

Many moons ago[1] I wrote this, which seems appropriate to share here:

    fn main() {
      println!(r#"{:X?}{}"#,
        __=(|&__@_:&'_ _,|->_{[(|(..,_,__,_,):(_,_,((),),)|__..__)(__)]})({&(!(({"\"__'\\\\\
        \'";(||{('\"');()})();}>=*&())|(|__|__||__|__)((()<())&(()>()))),&[..=..],({0__.%-//
        0.;(|_:[();0],|{})([[],[],][0]);},),)}),_={(|_0_:[_;0],_:&[()]|{;_0_})({{[0;0]}},&[[
        ]][(0..)][{..}][0],);""},);
    }

[1]: https://www.reddit.com/r/rust/comments/8p013f/comment/e094qj...

benreesman• 1 year ago

I'm actually working on a project I'm quite serious about but jokingly refer to as "Ergonomic Rust", which would make all of it a weird expression in Rust.

It's a C++23 library suite and lint set that eliminates:

- UB in all but the most contrived cases (I think I can get it to zero with a modest clang patch set) - bounds errors (see below) - bans all naked pointers and most references of any kind (NVRO and elision are mandated since 17, and on modern hardware like `znver5` you're usually pessimizing with e.g. `const foo_t& foo`) - and has no `usafe` keyword to fall back on, that's enforced at the conceptual module level by having things declare they are unsafe in their entirety via `extern "C"`

This stuff is really unlocked by C++23:

``` template<typename T> concept SafeIndexable = requires(T& t, const T& ct, size_t idx) { { t.at(idx) } -> std::same_as<typename T::reference>; { ct.at(idx) } -> std::same_as<typename T::const_reference>; // Banned: t[idx] };

// Wrapper that forces .at() usage template<SafeIndexable Container> class Safe { Container c; public: // Forward everything except operator[] template<typename... Args> Safe(Args&&... args) : c(std::forward<Args>(args)...) {}

    // Evil genius move: operator[] calls .at()
    auto operator[](size_t idx) -> decltype(auto) {
        return c.at(idx);  // Throws on bounds violation!
    }
    
    auto operator[](size_t idx) const -> decltype(auto) {
        return c.at(idx);
    }
    
    // Forward other operations
    auto begin() { return c.begin(); }
    auto end() { return c.end(); }
    // ... etc

};

// Usage: Safe<std::vector<int>> vec{1, 2, 3}; vec[10]; // Throws std::out_of_range instead of UB! ```

Weird Expressions in Rust

Related Stories