CODEWITHSUNDEEP
rubysyntax
poorvank
poorvank

Reputation: 7602

use of ! in Ruby

I am new to ruby! And i am trying to learn the use of "!" .

I am aware that ! is included to so that the user's string is modified in-place; otherwise, Ruby will create a copy of user_input and modify that instead.

But in the following case for both the programs i am getting the same output.Why?

print "Please Enter your Input"
user_input = gets.chomp
user_input.downcase!

print "Please Enter your Input"
user_input = gets.chomp
user_input.downcase

Upvotes: 1

Views: 171

Answers (3)

James Brewer
James Brewer

Reputation: 1755

In Ruby, bangs (!) are used to inform the programmer that the method they are calling is destructive. It's Ruby's way of saying "Hey! This method is going to change the object it is called on!". A number of safe methods in the String, Array,Enumerable`, etc classes have destructive counterparts.

Example:

my_str = "Hello, World!"
my_str.downcase # => "hello, world!"
my_str # => "Hello, World!"

my_str = "Goodbye, World!"
my_str.downcase! # => "goodbye, world!"
my_str #> "goodbye, world!"

As you can see, while both methods return the string's lower case variant, downcase! actually changes my_str permanently.

It's a very convenient aspect of Ruby that I wish more languages offered.

I think it's also worth mentioning that, because destructive methods work in-place, they are generally faster and more memory efficient than their safe counterparts who have to return new objects. Therefore, my_string.downcase! should be preferred to my_string = my_string.downcase whenever possible.

Upvotes: 4

David
David

Reputation: 1191

Both methods behave the same, but the returned objects are different.

downcasereturns a modified copy of user_input. In other words, user_input stays the same.

downcase! returns user_input modified. Note that this can be more memory efficient, since you don't generate a copy of user_input.

In both cases, they return a downcase version of user_input. That's why you have the same output.

To learn more about bang methods in Ruby, see this blog post.

hth

Upvotes: 1

Alberto Zaccagni
Alberto Zaccagni

Reputation: 31560

print "Please Enter your Input"
user_input = gets.chomp
user_input.downcase!

user_input value is what the user entered, in lowercase

print "Please Enter your Input"
user_input = gets.chomp
user_input.downcase

user_input value is what the user entered

The difference resides in the value of user_input, not in what gets printed.

Upvotes: 1

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