In Rust, 'for loops' can print all the values in a Rust range, but {:?} does not print all the values in a range

I tried creating a range with let myvar =1..5;, and then printing it out with both the {:?} formatter and a for loop. If I understand correctly, ranges are iterators in Rust, if {:?} can be used to print out all the values in an array, it should be able to do the same for a range.

However, when I tried running these in my main function:

let myvar=1..5;
println!("{:?}",myvar);

for i in myvar{
println!("{i}");
}

I got these results instead.

1..5 

1
2
3
4

What I expect is to see 1234 for the range values printed out by {:?} formatter instead of 1..5. I'm running rustc 1.69.0 (84c898d65 2023-04-16).

I apologize in advance if this is a basic question, as I have searched in quite a few places and could not find an issue like this (either that, or I'm just not searching with the correct terms).

> if {:?} can be used to print out all the values in an array, it should be able to do the same for a range

All {:?} does is format the value using the value's implementation of the Debug trait. It is up to the value's implementation to decide how to represent the value.

Simply, the array type and range types implement this trait differently. I would argue that the implementation for ranges is more useful than printing out all of the values in the range. Consider a huge range like 1..1000000. If you are trying to inspect a range during debugging to see what it contains, displaying the endpoints of the range is substantially more useful than dumping every value the range semantically contains. More generally, during debugging you usually care more about the value's state and less about what the value does under certain circumstances.

It's also worth noting that there is no blanket implementation of Debug for all iterators -- individual iterator types can choose to implement Debug, or choose not to.

It does not make much sense for a range to print out every element for its debug output.

For one, a range is not always used as a sequence of numbers; it is equally used to represent the some "bounds". It would be annoying to debug a rectangle that exists in space between x: 10..100 and y: 40..60 if that output contained each individual number. Also used as bounds when passed to .range() on BTreeMaps.

Secondly, an array represents a collection of elements and thus when debugging it would be helpful to know what those elements are. A range on the otherhand is not a collection and you do not need to explicitly show what all values are within that range. Its trivial to see it would "contain" elements larger than the starting value, and less than the ending value.

Thirdly, Rust iterators in general are lazy and read-once; they require modification to progress and yield each element. It would be unexpected for a debug statement to exhaust the underlying iterator (and not possible in general without interior mutability). Range could make an exception since it is trivially clonable, but that is not a property of all iterators.