What is the data type of [email protected] in BASH?

Question

bash

Slowly I encounter various subtleties of BASH and have reached a dead end. I just can't figure out a simple thing - what is the data type of [email protected] and ${somearray[@]}? More precisely, not even so, the first question is: is it true that [email protected] is completely similar in behavior and usage to ${somearray[@]}? (where somearray is some array).
And the second question, in fact - what data type does [email protected] have and, most importantly, where can I read comprehensive information on how to work with this data type and what does its use in different situations lead to?
Let me explain: there are tricks like ${@: -1}. If [email protected] were a string, then such a construction would return the last character. And it returns the last element of the array, in the case of [email protected] - the last element of a generally non-existent array of all input arguments.
Please clarify what kind of animal this is, how to work with it, and most importantly - what opportunities does it have?
As I understand it, [email protected] is some intermediate pseudo-type, something between an array and a string, which cannot be obtained by external means. [email protected] almost always pretends to be a string of space-separated components, and the only unique property I've found of it is ${@: N} - cutting off the first or last N components. Nothing more intelligible could be dug up / thought up. I really appreciate the help, I would like to understand.

Answer 1

In general, it is rather an untyped array, the value type of any member of which depends on the interpretation. In general, all arrays in bash can be considered untyped.

#!/bin/bash
echo [email protected]
array=()
[email protected]
echo ${array[@]}

If this script is run like this:
this code will output the following:

1 2 3 4 5
1 2 3 4 5

If so:
then the following:

1 2 3 4 5
1 2 3 4 5

As you can see, this is essentially the same thing, although it is represented definitely, it would seem, by numeric values ​​in the first case and string values ​​in the second.