It's also the concepts. The comment from fauigerzigerk sums it up well. You just have to know via experience, a great teacher, or very attentive learning that

It's also the concepts. The comment from fauigerzigerk sums it up well. You just have to know via experience, a great teacher, or very attentive learning that vec![1,2,3] is going to pop all of its values in a "print elements" loop while [1,2,3] will retain each value. Other languages have similar behavior, but it's often more obvious e.g. Python with the .next() keyword.