Symbols
A typical implementation of a Ruby interpreter maintains a symbol table in which it stores the names of all the classes, methods, and variables it knows about. This allows such an interpreter to avoid most string comparisons: it refers to method names (for example) by their position in this symbol table. This turns a relatively expensive string operation into a relatively cheap integer operation.
These symbols are not purely internal to the interpreter; they can
also be used by Ruby programs. A Symbol
object refers to a symbol. A symbol
literal is written by prefixing an identifier or string with a
colon:
:symbol # A Symbol literal :"symbol" # The same literal :'another long symbol' # Quotes are useful for symbols with spaces s = "string" sym = :"#{s}" # The Symbol :string
Symbols also have a %s
literal syntax that allows arbitrary delimiters in the same way
that %q
and %Q
can be used for string literals:
%s["] # Same as :'"'
Symbols are often used to refer to method names in reflective
code. For example, suppose we want
to know if some object has an each
method:
o.respond_to? :each
Here’s another example. It tests whether a given object responds to a specified method, and, if so, invokes that method:
name = :size if o.respond_to? name o.send(name) end
You can convert a String
to a
Symbol
using the intern
or to_sym
methods. And you can convert a Symbol
back into a String
with the to_s
method or its alias id2name
:
str = "string" # Begin with a string sym = str.intern # Convert ...
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