String#to_sym

str.to_sym -> symbol

The to_sym method converts a string to its corresponding symbol. Symbols are immutable, interned strings that are efficient for use as hash keys, identifiers, and method names. Each unique string maps to a single symbol object, making to_sym useful for de‑duplication and fast comparison.

Syntax

str.to_sym

The method takes no parameters. It returns a Symbol whose #to_s representation equals the original string.

Parameters

to_sym has no parameters.

Examples

Basic conversion

"hello".to_sym
# => :hello

"foo_bar".to_sym
# => :foo_bar

"123".to_sym
# => :"123"  (symbol with numeric characters)

Symbols are interned

a = "hello".to_sym
b = "hello".to_sym
a.object_id == b.object_id
# => true (same symbol object)

c = "world".to_sym
d = "world".to_sym
c.object_id == d.object_id
# => true

Edge cases: empty string and whitespace

"".to_sym
# => :"" (empty symbol)

"   ".to_sym
# => :"   " (symbol containing spaces)

Non‑ASCII characters

"café".to_sym
# => :café

"🎉".to_sym
# => :🎉

Using symbols as hash keys

hash = { "name" => "Alice", "age" => 30 }
hash.keys.map(&:to_sym)
# => [:name, :age]

Common Patterns

Converting user input to symbols for configuration

def parse_option(input)
  case input.to_sym
  when :enable
    true
  when :disable
    false
  else
    raise "Unknown option: #{input}"
  end
end

parse_option("enable")   # => true
parse_option("disable")  # => false
parse_option("invalid")  # => raises "Unknown option: invalid"

De‑duplicating strings in a collection

strings = ["foo", "bar", "foo", "baz", "bar"]
symbols = strings.map(&:to_sym).uniq
# => [:foo, :bar, :baz]

Symbolizing hash keys (Rails‑style)

def symbolize_keys(hash)
  hash.transform_keys(&:to_sym)
end

symbolize_keys({ "name" => "Alice", "age" => 30 })
# => {:name=>"Alice", :age=>30}

Fast lookup with symbol keys

LOOKUP = { :en => "English", :fr => "French", :es => "Spanish" }

def translate(lang)
  LOOKUP[lang.to_sym] || "Unknown"
end

translate("en")   # => "English"
translate("fr")   # => "French"
translate("de")   # => "Unknown"

Errors

to_sym does not raise exceptions for any string input. However, note that symbols are not garbage‑collected in Ruby versions before 3.2, so converting uncontrolled user input to symbols can lead to a memory leak (symbol DoS). In Ruby 3.2 and later, dynamic symbols are garbage‑collected.

Potential memory concerns (pre‑3.2)

# In Ruby < 3.2, repeated conversion of arbitrary strings can cause memory growth
loop do
  SecureRandom.hex(10).to_sym
end

See Also

• String#encode
• String#unpack
• String#unpack1