address = [1,2,3]
p address
new_address = address.reverse!
p new_address
p address.reverse!

Prints:

[1,2,3]
[3,2,1]
[1,2,3]

I don't understand why the last print out is 1,2,3 if it is meant to print the address in reverse, the address is 1,2,3

I expected the last line to be [3,2,1].

CodePudding user response：

To understand why this behavior you need to know what the ! means:

It indicate to the interprete that has to operate over the object and make the changes on it first and then return the result.

So address is:

address = [1,2,3]

When you call this:

new_address = address.reverse! # Address is [3,2,1]

And last:

p address.reverse! # address is [1, 2, 3]

Here the base is to understand that ! is always modifiying the object itself.

CodePudding user response：

In ruby when you have a ! at the end of the method call that means that it changes the recipient as well.

So new_address = address.reverse! not just assigned the reverted value to new_address but also to address.

I updated your code to make it more visible:

address = [1,2,3]
p address
new_address = address.reverse! # [3,2,1]

p address # [3,2,1]
p new_address # [3,2,1]

p address.reverse! # [1,2,3]

What you wanted to use is the same method but without !

address = [1,2,3]
p address
new_address = address.reverse
p new_address
p address.reverse

More info: http://ruby-for-beginners.rubymonstas.org/objects/bangs.html

CodePudding user response：

It's all about the bang (!) in ruby.

address = [1,2,3]
p address
#> [1,2,4]

address.reverse
p address
#> [1,2,3]

address.reverse!
p address
#> [3,2,1]

Bang or exclamation mark means that you are making a permanent saved change in your code.

some more examples:

#without Bang (!).
name = "Ruby Monstas"
puts name.downcase
#> ruby monstas

puts name 
#> Ruby Monstas


# With Bang(!) Operator
name = "Ruby Monstas"
puts name.downcase!
#> ruby monstas

puts name
#> ruby monstas