Re: I'm confused about Ruby.2.5.3 Method#arity for Dir.entries and Dir#entries

On Wed, Oct 23, 2019 at 8:03 AM Danielle Velie <[email protected]>
wrote:

> Can you please explain to me what is going on sir with the program thank
> you so much Danielle Lee Ramos
>

My apologies for my delay on responding. I hope the following helps, and
isn't too little explanation. Or too much! (I don't know how much
experience you have with Ruby.)

I ran Interactive Ruby (irb) and JRuby Interactive Ruby (jirb) as a simple
way of demonstrating what I was asking.
I use comments like "#=> ..." to show the result of a command.
The results shown below are for "Microsoft Windows" Ruby irb;I also show
the results for JRuby jirb if that is different

For more information on the method calls I made:
* String#chomp:   https://ruby-doc.org/core-2.5.3/String.html#method-i-chomp
* String#length:
https://ruby-doc.org/core-2.5.3/String.html#method-i-length
* Dir.entries:    https://ruby-doc.org/core-2.5.3/Dir.html#method-c-entries
* Dir#entries:    I couldn't find documentation for this Public Instance
Method;
                  I don't know why not.
* Encoding:       https://ruby-doc.org/core-2.5.3/Encoding.html

# First I give information about the Ruby version I'm using:
RUBY_PLATFORM  #=> "x64-mingw32"    #JRuby #=> "java"
RUBY_VERSION   #=> "2.5.3"

# Next I chose a Ruby method to show how I think Method#arity works;
# I decided to use String#chomp.
# First I show how it behaves with different numbers of arguments,
# then I show the (actual - and expected!) result of s.method(:chomp).arity,
# and also of s.method(:length).arity because I know String#length has
arity 0.
#
# I also show that to get the arity of a method of an object of a class
# we need to call method(:method_name).arity on the object, not the class.
# I did that because as well as Dir objects having an instance method
"entries"
# the Dir class itself has a singleton method also called "entries",
# and I wanted to ensure I knew which method I was getting the arity for.

String.method(:chomp)  #=> undefined method 'chomp' for #<Class:String>
s = "str*"       #=> "str*"
s.chomp()        #=> "str*"
s.chomp("?")     #=> "str*"
s.chomp("*")     #=> "str"
s.chomp("*", 1)  #=> wrong number of arguments (given 2, expected 0..1)
s.method(:length).arity  #=> 0   # as expected: needs 0 arguments
s.method(:chomp).arity   #=> -1  # as expected: needs 0 or 1 arguments

# I had found that in JRuby 2.5.3 Dir.entries could have an optional
argument
# of the string Encoding to be used, but that this was not the case
# for my Ruby 2.5.3. So I set up an Encoding object.
Encoding.find("filesystem")  #=> #<Encoding:Windows-1252>
enc = Encoding::ASCII_8BIT   #=> #<Encoding:ASCII-8BIT>

# Now I call both the instance method "entries" of Dir objects,
# and the singleton method "entries" of the Dir class,
# showing the results of different combinations of arguments,
# and the results of finding the arity of those "entries" methods.
# These also show where the behaviour of Ruby and JRuby differ.
d = Dir.new(".")            #=> #<Dir:.>
Dir.method(:entries).arity  #=> -1  # implying n = 0 so can accept 0
arguments
d.method(:entries).arity    #=> -1  # implying n = 0 so can accept 0
arguments
d.method(:entries).arity  #JRuby #=> 0 # implying n = 0 so must have 0
arguments
Dir.entries(".")         #=> [ array of files in "." ]
Dir.entries(".", enc)    #=> wrong number of arguments (given 2, expected 1)
                         #JRuby #=> [ array of files in "." ]
Dir.entries(".", enc, 3) #=> wrong number of arguments (given 3, expected 1)
                  #JRuby #=> wrong number of arguments (given 3, expected
1..2)
Dir.entries()     #=> wrong number of arguments (given 0, expected 1)
                  #JRuby #=> wrong number of arguments (given 0, expected
1..2)
d.entries()            #=> [ array of files in "." ]
d.entries(enc)         #=> wrong number of arguments (given 1, expected 0)


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