I think you are wrong. I looked and in Rust doc it says that: "Removes the last element from a vector and returns it, or None if it is empty". You better be doing check for "None".
Depends what you mean by explicit.
Look at it like this:
pub fn main() {
let mut vec : Vec<i32> = vec![];
let x = vec.pop();
println!("{:?}",x); // prints: None
}
vec.pop().expect("I want a value")
if let Some(x) = vec.pop() {
println!("{:?}",x);
} else {
println!("EMPTY"); // prints: Empty
}
Types like Result will issue warning that you didn't handle the cases.
I looked at your example and played a bit with it and yes I agree with you - compiler does help in this case.
My old text:
So instead of checking if vector is not empty you check that the return result is not empty. I do not see much difference. If Rust compiler would choke when "else" clause in your example is not present I would understand your point about compiler preventing improper access.
> If Rust compiler would choke when "else" clause in your example is not present
The compiler won't choke, but it will stop you from accessing the value.
It doesn't matter if you omit the `else` clause or not, the type system ensures that you can't access invalid values.
Here's a bit of an example based off of @Ygg2's code: https://play.rust-lang.org/?version=stable&mode=debug&editio...
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Rust does that with the combination of "sum types" (aka "enums with data") and pattern matching. An `Option<T>` is either `Some(T)` or `None`. Matching on an option with the pattern `Some(value)` creates a new syntactic scope where the value is accessible. This scope is only entered if the `Option` is actually non-empty.
All ways of getting the value from the option are ultimately shorthand for a match in that way. For example, option.unwrap() will either get the value if it there, or panic. Option.unwrap_or(x) will either get the value of it there, or use x instead.
In practice this is x100 less error prone than C++. Source: was burned by vector.front() on empty vectors more than once. In C++, UB. In rust, usually the "empty case" is considered when first writing the code, or at least caught during review (unwraps tend to be very visible in reviews)
I'm not a C++ expert but here is my understanding. Vector is essentially a tuple of (dynamic_array_address: ptr, size: size_t, capacity: size_t). To pop a value from vector you just decrements size. So what happens when you have empty vec? Your size is 0, and you're substracing 1, which causes undefined behavior.
Correct way is to check BEFORE you pop_back().
In Rust, any number of invocation of pop() will not result in undefined behavior. You can ignore the value, or you can check it, but it doesn't expose you to UB just for slightly misusing a vector.
Absolutely and this is exactly what I do. I always check the containers before removing elements.
>"In Rust, any number of invocation of pop() will not result in undefined behavior. You can ignore the value, or you can check it, but it doesn't expose you to UB just for slightly misusing a vector."
I do not understand "slightly misusing" part. I assume in Rust it would bomb if pop() returns "none" and you try for example add said "none" to some number.
That's the thing. It wouldn't. Worse you can do is make whole program panic, with well defined stack trace and message.
It will never return non-sense and pretend all is ok.