Ruby Language Symbols
Syntax
- :symbol
- :'symbol'
- :"symbol"
- "symbol".to_sym
- %s{symbol}
Remarks
Advantages of using symbols over strings:
1. A Ruby symbol is an object with O(1) comparison
To compare two strings, we potentially need to look at every character. For two strings of length N, this will require N+1 comparisons
def string_compare str1, str2
if str1.length != str2.length
return false
end
for i in 0...str1.length
return false if str1[i] != str2[i]
end
return true
end
string_compare "foobar", "foobar"
But since every appearance of :foobar refers to the same object, we can compare symbols by looking at object IDs. We can do this with a single comparison.(O(1))
def symbol_compare sym1, sym2
sym1.object_id == sym2.object_id
end
symbol_compare :foobar, :foobar
2. A Ruby symbol is a label in a free-form enumeration
In C++, we can use “enumerations” to represent families of related constants:
enum BugStatus { OPEN, CLOSED };
BugStatus original_status = OPEN;
BugStatus current_status = CLOSED;
But because Ruby is a dynamic language, we don’t worry about declaring a BugStatus type, or keeping track of the legal values. Instead, we represent the enumeration values as symbols:
original_status = :open
current_status = :closed
3. A Ruby symbol is a constant, unique name
In Ruby, we can change the contents of a string:
"foobar"[0] = ?b # "boo"
But we can’t change the contents of a symbol:
:foobar[0] = ?b # Raises an error
4. A Ruby symbol is the keyword for a keyword argument
When passing keyword arguments to a Ruby function, we specify the keywords using symbols:
# Build a URL for 'bug' using Rails.
url_for :controller => 'bug',
:action => 'show',
:id => bug.id
5. A Ruby symbol is an excellent choice for a hash key
Typically, we’ll use symbols to represent the keys of a hash table:
options = {}
options[:auto_save] = true
options[:show_comments] = false
