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...
Hacker News will try and discourage really quick back and forth comments. To do so, the reply button is hidden. However, if you click on the timestamp, to go to the comment's own page, you can reply there.
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)