[ruby-core:82962] [Ruby trunk Bug#13937][Rejected] ARGV doesn't behave like an array

Issue #13937 has been updated by jeremyevans0 (Jeremy Evans).

Status changed from Open to Rejected

lucascaton (Lucas Caton) wrote:
> Ruby allows us to access an array item by passing its index, regardless if there is or not a space between the array and the [] with the index.
> Ie.: both of the following lines work:
> 
> ~~~ ruby
> [][0] # nil
> [] [0] # nil
> ~~~
> 
> **ARGV** is an array as well. However, it doesn't work when we add a space to access some index:
> 
> ~~~ ruby
> ARGV # []
> ARGV.class # Array
> ARGV == [] # true
> ARGV[0] # nil
> ARGV [0] # NoMethodError: undefined method `ARGV' for main:Object
> ~~~
> 
> The last line should've returned **nil**.
> 
> Ps.: Same happens when you call a file with arguments by running **$ ruby file.rb foo bar**.
> **ARGV [0]** will also raise an exception.

This isn't a bug, you just need to understand how the parser works.

`ARGV[0]` is parsed as `(ARGV)[0]`, a constant reference and then calling `[]` with the argument `0` on that reference.  It's similar to `Object.const_get(:ARGV).public_send(:[], 0)`.

`ARGV [0]` is parsed as `ARGV([0])`, calling the `ARGV` method with a single argument being the array `[0]`.  It's similar to to `send(:ARGV, [0])`. You get the NoMethodError here because no method named `ARGV` has been defined.

This issue isn't related to `ARGV` specifically, any constant or method called without arguments will have similar behavior:

~~~ruby
A = [1]
A[0] # 1
A [0] # NoMethodError
def a; [1] end
a[0] # 1
a [0] # ArgumentError
~~~

----------------------------------------
Bug #13937: ARGV doesn't behave like an array
https://bugs.ruby-lang.org/issues/13937#change-66861

* Author: lucascaton (Lucas Caton)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin16]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
Ruby allows us to access an array item by passing its index, regardless if there is or not a space between the array and the [] with the index.
Ie.: both of the following lines work:

~~~ ruby
[][0] # nil
[] [0] # nil
~~~

**ARGV** is an array as well. However, it doesn't work when we add a space to access some index:

~~~ ruby
ARGV # []
ARGV.class # Array
ARGV == [] # true
ARGV[0] # nil
ARGV [0] # NoMethodError: undefined method `ARGV' for main:Object
~~~

The last line should've returned **nil**.

Ps.: Same happens when you call a file with arguments by running **$ ruby file.rb foo bar**.
**ARGV [0]** will also raise an exception.



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