Are strings in Ruby mutable?

ruby string immutability mutable
SundayMonday picture SundayMonday · Dec 20, 2011 · Viewed 13.5k times · Source

Consider the following code:

$ irb
> s = "asd"
> s.object_id   # prints 2171223360
> s[0] = ?z     # s is now "zsd"
> s.object_id   # prints 2171223360 (same as before)
> s += "hello"  # s is now "zsdhello"
> s.object_id   # prints 2171224560 (now it's different)

Seems like individual characters can be changed w/o creating a new string. However appending to the string apparently creates a new string.

Are strings in Ruby mutable?

Answer

Marek Příhoda picture Marek Příhoda · Dec 20, 2011

Yes, strings in Ruby, unlike in Python, are mutable.

s += "hello" is not appending "hello" to s - an entirely new string object gets created. To append to a string 'in place', use <<, like in:

s = "hello"
s << "   world"
s # hello world

Related questions

Are strings mutable in Ruby?

Are Strings mutable in Ruby? According to the documentation doing str = "hello" str = str + " world" creates a new string object with the value "hello world" but when we do str = "hello" str << " world" It does not mention that …

Read More
Ruby: What does the comment "frozen_string_literal: true" do?

This is the rspec binstub in my project directory. #!/usr/bin/env ruby begin load File.expand_path("../spring", __FILE__) rescue LoadError end # frozen_string_literal: true # # This file was generated by Bundler. # # The application 'rspec' is installed as part …

Read More
How to check whether a string contains a substring in Ruby

I have a string variable with content: varMessage = "hi/thsid/sdfhsjdf/dfjsd/sdjfsdn\n" "/my/name/is/balaji.so\n" "call::myFunction(int const&)\n" "void::secondFunction(char const&)\n" . . . "this/is/last/line/liobrary.so" In the …

Read More