Ruby syntaxes

ruby-syntaxes.md

Program-global

• # frozen_string_literal
• # encoding
• __END__

Expressions

• Singleton literals
  • nil
  • true
  • false
• Numeric literals
  • 123
  • 123.0
  • 123r
  • 123i
• String-likes
  • /re/ (w/ or w/o interpolation)
  • "str" (w/ or w/o interpolation)
  • :"sym" (w/ or w/o interpolation)
  • :sym
  • #{expr}
  • #@var
  • %w[...] and its family
  • <<EOF and its family
• Constructor syntaxes
  • [elems]
  • { entries }
  • .. / ...
• Variable-likes
  • my_var
  • MyConst
  • :: (prefix)
  • :: (infix)
  • @var
  • @@var
  • $foo
    • $foo
    • $" etc.
    • $-a etc.
    • $&
    • $1
  • self
  • __ENCODING__
  • __FILE__
  • __LINE__
  • it
  • _1
• Calls
  • meth
  • obj.meth (also &. and ::)
  • obj.(args) (also &. and ::)
  • obj[idx]
  • `cmd` (w/ or w/o interpolation)
  • -> { body }
  • for lhs in arr
  • super (which is super(...))
  • super(args)
• Operators
  • && / and
  • &&=
  • || / or
  • ||=
  • ! / not (has special semantics in old Rubies)
  • Ordinary operator expressions (which is method call)
    • ! / ~ / + (unary) / - (unary)
    • **
    • * / / / %
    • + / -
    • << / >>
    • &
    • | / ^
    • >, >=, <, <=
    • <=>, ==, !=, ===, =~, !~
    • not (alias of !)
  • Operator assignments (for binary non-predicate operators)
    • **=
    • *= / /= / %=
    • += / -=
    • <<= / >>=
    • &=
    • |= / ^=
• Declarations
  • def meth (also endless variants)
  • def (recv).meth (also endless variants)
  • class
  • class <<expr
  • module
  • alias
  • undef
• Controls
  • begin
  • if / unless (either prefix or infix)
  • else / elsif
  • while / until (either prefix or infix)
  • case / when / else (for classic switching)
  • case / in / else (for pattern-based switching)
  • ensure
  • rescue
  • rescue (infix operator)
  • return
  • break
  • next
  • yield
  • redo
  • retry
  • END
  • BEGIN
• Arguments (also in Arrays and Hashes)
  • arg_expr as in arguments
  • *arr
  • key => value
  • key: value
  • **kwargs
  • &my_block
  • do |params| end / { |params| }
  • ... as in arguments
• Predicates
  • defined?
  • expr in pat
  • expr => pat
• Implicit syntaxes
  • Implicit array in assignment RHS
  • if a..b (i.e. flip-flop)
  • if /re/ (a.k.a. match last)
  • /(?<my_var>...)/ =~ val (note the capture)

LHS

• Variable-likes
  • my_var
  • my_param = default_value
  • my_kwparam:
  • my_kwparam: default_value
  • MyConst (also note ::)
  • # shareable_const_value: literal
  • @var
  • @@var
  • $var (except $1 and $& variants)
• Calls
  • obj.attr
  • obj[idx]
• Splats
  • *args
  • **kwargs
  • **nil
  • ...
• Multi
  • lhs1, lhs2
• Decl
  • do |x, y; z|
• Implicit syntaxes
  • implicit it capture (when the variable is used in the block body)
  • implicit _1 capture (when the variable is used in the block body)
  • implicit * (when the multi LHS ends with ,)

Patterns

• |
• [elems]
• [*left, elems, *right]
• my_var
• { entries }
• ^(expr) / ^my_var