Passing an gets.chomp as an argument

Question

input_file = ARGV.first

def print_all(f)
    puts f.read
end

def rewind(f)
    f.seek(0)
end

def print_a_line(line_count, f)
    puts "#{line_count}, #{f.gets.chomp}"
end

current_file = open(input_file)

puts "First let's print the whole file:¥n"

print_all(current_file)

puts "Let's rewind kind a like a tape"

rewind(current_file)

puts "Let's print three lines:"

current_line = 1
print_a_line(current_line, current_file)

current_line += 1
print_a_line(current_line, current_file)

I'm sure there is a kinda similar post to this, but my question is a bit different. As seen above, the print_a_line method got two params that are line_count and f.

1) As I understood, line_count argument only serves as a variable which is current_line and it is just an integer. How does it relate to the rewind(f) method because when I run the code, the method print_a_line shows this:

1, Hi
2, I'm a noob

where 1 is the first line and 2 is the second. line_count is just a number, how does ruby know that 1 is line 1 and 2 is line 2?

2) Why use gets.chomp in method print_a_line? If I pass just f like this

def print_a_line(line_count, f)
    puts "#{line_count}, #{f}"
end

I'll get a crazy result which is

1, #<File:0x007fccef84c4c0>
2, #<File:0x007fccef84c4c0>

Answer 1

Because IO#gets reads next line from readable I/O stream(in this case it's a file) and returns a String object when reading successfully and not reached end of the file. And, chomp removes carriage return characters from String object.

So when you have a file with content such as:

This is file content.
This file has multiple lines.

The code will print:

1, This is file content.
2, This file has multiple lines.

In the second case, you're passing file object itself and not reading it. Hence you see those objects in output.