Node Types

This is a partial list of the node types parsed by the AST and corresponding methods and information associated with them.

RuboCop::AST::Node defines some additional methods on certain node types by giving them a separate class. You can see the method definitions in the API documentation.

For full information, please see the parser documentation. This page will act as a quick index to that page, which has more examples and fuller explanation of the different location pieces. You can also see a full AST for yourself by running ruby-parse --legacy -L -e "ruby(code: 'here')".

There are a few "meta-types" of nodes that will be mentioned in descriptions:

  • Expression nodes: any expression that returns a value - variables (lvar, ivar, cvar etc.), send or csend, const, self, any literal value (int, str, nil, etc.), or control statements like if, case, begin, etc.

  • Assignment nodes: Any node that assigns a value. lvasgn, ivasgn, cvasgn, gvasgn, send (e.g. self.foo = 5), or csend.

  • Body statement: This can be essentially any node except those that must be nested (like args or mlhs). Typically it comes as the children of a node that can contain arbitrary code, like def or class. This will always be a single node which is either an expression, a begin node, or nil.

Location Information

There are different parts of the source map you can get from the node, by calling .loc on it. Every node has an expression value which usually represents the entire node, but others have additional fields.

The following fields are given when relevant to nodes in the source code:

Field

Description

assoc

The fat-arrow: ⇒ used in the body of rescue clauses (resbody), not in a hash pair)

begin

  • Start of parentheses or square brackets ( or [

  • Start of do..end blocks (containing the do keyword)

  • then keyword

  • begin keyword

  • The first symbol in literals (like " for strings or : for symbols)

colon

The : symbol, used as part of a ternary (:)

dot

The . or &. operator used for send and csend nodes.

double_colon

The :: operator

else

The else or elsif keyword

end

  • End of parentheses or square brackets ) or ]

  • The end keyword

  • The last symbol in literals (like " for strings)

heredoc_body

The body of a string in heredoc format.

heredoc_end

The end of the heredoc statement.

in

The in keyword (as in for..in)

keyword

Any text-based keyword, like begin or and, with the exception of other keywords handled by other fields. This will include the full string containing the keyword.

name

Used when defining something (like const or arg).

operator

Any symbol representing an operator, like * (splat) or ||=.

question

The ? symbol used as part of a ternary (if)

selector

Used for method invocation (send / csend) or operators that are actually methods (like +)

Node Types

Type Description Children Example Node Class

alias

Method alias

Two children - both are sym, dsym or gvar nodes.

alias :foo :bar

AliasNode

and

And operator

Two children are both expression nodes representing the operands.

a and b && c

AndNode

and_asgn

And-assignment (AND the receiver with the argument and assign it back to receiver).

First child must be an assignment node, second child is the expression node.

a &&= b

AndAsgnNode

arg

Required positional argument. Must come inside an args.

One child - a symbol, representing the argument name.

def foo(bar)

ArgNode

args

Argument list. Must come inside a def, defs, or block node.

Children must be arg, optarg, restarg, blockarg, kwarg, kwoptarg, kwrestarg, kwnilarg, or forwardarg.

def whatever(foo, bar=1, baz: 5)

ArgsNode

array

Array literal.

The values in the array, including a possible splat.

[1, 2, 3]

ArrayNode

back_ref

Regular expression back-reference, e.g. $&.

One child (symbol) representing the reference name, e.g. :$&.

re = /foo(abc)/; $&

N/A

block

Block execution.

Three children. First child is the receiver or a lambda node; second child is args or forward_args (only if emit_forward is false; it’s true by default); third child is a body statement.

foo.bar do |a, b|; puts a; end

BlockNode

block_pass

Used when passing a block as an argument.

One child, an expression node representing the block to pass.

foo(a, &my_block)

N/A

blockarg

Reference to block argument from a function definition. Must come inside an args.

One child - a symbol, representing the argument name.

def foo(&bar)

ArgNode

break

break keyword

One child with an expression node for the results to be passed through the break.

break 1

BreakNode

case

Case statement.

First child is an expression node for the condition to check. Last child is an expression node for the "else" condition. All middle nodes are when nodes.

case a; when 1; b; when 2; c; else d; end

CaseNode

casgn

Constant assignment

Three children: the parent object (either an expression, nil or cbase), the constant name (a symbol), and the expression being assigned.

Foo::Bar = 5

CasgnNode

cbase

Represents the top-module constant (i.e. the '::' before a constant name). Only occurs inside a const node.

None

::Foo

N/A

complex

Complex literal

One child, the Complex value

1i

N/A

const

Constant reference.

Two children, the parent object (either an expression, nil or cbase) and the constant name (a symbol).

AModule::AClass

N/A

class

Class definition

Three children. First child is a const node for the class name, second child is a const node for the parent name, or nil, third child is a body statement.

class Foo < Bar; end

ClassNode

csend

Null-safe method invocation, i.e. using &.

First child is the receiver node (e.g. self), second child is the method name (e.g. :foo=) and the remaining children (if any) are nodes representing arguments.

foo&.bar

SendNode

cvar

Class variable access

One child, the variable name :@@cfoo

@@cfoo

VarNode

cvasgn

Class variable assignment

Two children: the variable name :@@foo and the expression being assigned

@@foo = 5

AsgnNode

def

Instance method definition (full format)

Three children. First child is the name of the method (symbol); second child is args or forward_args (only if emit_forward is false, and it’s true by default), and the last child is a body statement.

def foo(some_arg, kwarg: 1); end

DefNode

defined?

defined? keyword.

One child, an expression.

defined?(foo)

N/A

defs

Singleton method definition (full format) - i.e. defining a method on a single object.

Four children. First child is the receiver; second child is the name of the method (symbol); third child is args or forward_args (only if emit_forward is false, and it’s true by default), and the fourth child is a body statement.

def some_obj.foo(some_arg, kwarg: 1); end

DefNode

dstr

Interpolated string literal.

Children are split into str nodes, with interpolation represented by separate expression nodes.

"foo#{bar}baz"

StrNode

dsym

Interpolated symbol literal.

Children are split into str nodes, with interpolation represented by separate expression nodes.

:"foo#{bar}baz"

N/A

ensure

Block that contains an ensure along with possible rescue`s. Must be inside a `def, defs, block or begin.

The last child is the body statement of the ensure block. If there is a rescue, it is the first child (and contains the body statement of the top block); otherwise, the first child is the body statement of the top block.

begin; foo; rescue Exception; bar; ensure; baz; end

EnsureNode

erange

Exclusive range literal

Two children, the start and end nodes (including nil for beginless/endless)

1…​2

RangeNode

false

False literal

None

false

N/A

float

Floating point literal

One child, the Float value

-123.5

FloatNode

for

for..in looping condition

Three children. First child is a lvasgn or mlhs node with the variable(s), second child is an expression node with the array/range to loop over, third child is a body statement.

for a in arr do foo; end

ForNode

forward_arg

Forwarding argument, for Ruby 3.0 (when emit_forward_arg is true). Must come inside an args node.

None

def whatever(foo, …​)

ArgNode

forward_args

Forwarding argument list, for Ruby 2.7 (when emit_forward_arg is false). Must come inside a def, or defs node.

None

def (foo(…​)

ForwardArgsNode

forwarded_args

Forwarding arguments into a method call

None

foo(…​)

N/A

forwarded_restarg

Forwarding positional arguments into a method call

None

foo(*)

N/A

forwarded_kwrestarg

Forwarding keyword arguments into a method call

None

foo(**)

N/A

gvar

Global variable access

One child, the variable name as a symbol :$foo

$foo

VarNode

gvasgn

Global variable assignment

Two children, the variable name :$foo and the expression being assigned

$foo = 5

AsgnNode

hash

Hash literal.

pair s and/or kwsplat s.

{ foo: 'bar' }

HashNode

if

If, else, elif, unless and ternary conditions

Three children. First child is the expression node representing the condition; second child is an expression node representing the true condition; third child is an expression, node representing the false condition. elif will nest another if node as the third child. question and colon location keys will only exist for ternaries.

if foo; bar; else; baz; end

IfNode

int

Integer literal

1, the integer value

-123

IntNode

ivar

Instance variable access

One child, the variable name :@foo

@foo

VarNode

ivasgn

Instance variable assignment

Two children, the variable name :@foo and the expression being assigned

@foo = 5

AsgnNode

irange

Inclusive range literal.

Two children, the start and end nodes (including nil for beginless/endless)

1..2

RangeNode

kwarg

Required keyword argument. Must come inside an args.

One child - a symbol, representing the argument name.

def foo(bar:)

ArgNode

kwbegin

Explicit begin block.

Child nodes are body statements.

begin,end

KeywordBeginNode

kwnilarg

Double splat with nil in function definition, used to specify that the function does not accept keyword args. Must come inside an args.

None

def foo(**nil)

N/A

kwoptarg

Optional keyword argument. Must come inside an args.

Two children - a symbol, representing the argument name, and an expression node for the value.

def foo(bar: 5)

ArgNode

kwsplat

Double splat used for keyword arguments inside a function call (as opposed to a function definition).

One child, an expression.

foo(bar, **kwargs)

KeywordSplatNode

kwrestargs

Double splat used for keyword arguments inside a function definition (as opposed to a function call). Must come inside an args.

One child - a symbol, representing the argument name, if a name is given. If no name given, it has no children..

def foo(**kwargs)

ArgNode

lvar

Local variable access

One child, the variable name

foo

VarNode

lvasgn

Local variable assignment

Two children: The variable name (symbol) and the expression.

a = some_thing

AsgnNode

masgn

Multiple assignment.

First set of children are all mlhs nodes, and the rest of the children must be expression nodes corresponding to the values in the mlhs nodes.

a, b, = [1, 2]

MasgnNode

mlhs

Multiple left-hand side. Used inside a masgn and block argument destructuring.

Children must all be assignment nodes or send nodes. Represents the left side of a multiple assignment (a, b in the example).

a, b = 5, 6

MlhsNode

module

Module definition

Two children. First child is a const node for the module name. Second child is a body statement.

module Foo < Bar; end

ModuleNode

next

next keyword

Zero or one child with an expression node for the results to be passed through the next

next 1

N/A

nil

Nil literal

None

nil

N/A

nth_ref

Regular expression capture group ($1, $2 etc.)

One child: The capture name, e.g. :$1

re = /foo(abc)/; $1

N/A

numblock

Block that has numbered arguments (_1) referenced inside it.

Three children. First child is a send/csend node representing the way the block is created, second child is an int (the number of numeric arguments) and the third child is a body statement.

proc { _1 + _3 }

BlockNode

op_asgn

Operator-assignment - perform an operation and assign the value.

Three children. First child must be an assignment node, second child is the operator (e.g. :+) and the third child is the expression node.

a +=

OpAsgnNode

optarg

Optional positional argument. Must come inside an args.

One child - a symbol, representing the argument name.

def foo(bar=1)

ArgNode

or

Or operator

Two children are both expression nodes representing the operands.

a or

OrNode

or_asgn

Or-assignment (OR the receiver with the argument and assign it back to receiver).

Two children. First child must be an assignment node, second child is the expression node.

a ||=

OrAsgnNode

pair

One entry in a hash.

Two children, the key and value nodes.

1 ⇒ 2

PairNode

rational

Rational literal

One child, the Rational value

2.0r

N/A

redo

Redo command

None

redo

N/A

regexp

Regular expression literal.

Children are split into str nodes, with interpolation represented by separate expression nodes. The last child is a regopt.

/foo#{bar}56/

RegexpNode

regopt

Regular expression option, appearing after a regexp literal (the "im" in the example).

A list of symbols representing the options (e.g. :i and :m)

/foo#{bar}/im

N/A

resbody

Exception rescue. Always occurs inside a rescue node.

Three children. First child is either nil or an array of expression nodes representing the exceptions to rescue. Second child is nil or an assignment node representing the value to save the exception into. Last child is a body statement.

begin; rescue Exception, A ⇒ bar; 1; end

ResbodyNode

rescue

A rescue statement.May be "top-level" or may be nested inside an ensure block (if both rescue and ensure are in the block).

First node is a body statement. Last child is the "else" body statement, or nil. Remaining children are resbody nodes.

begin; rescue Exception, A ⇒ bar; 1; end

restarg

Positional splat argument. Must come inside an args.

One child - a symbol, representing the argument name (if given). If no name given, there are no children.

def foo(*rest)

ArgNode

return

Return statement

Zero or one child, an expression node for the value to return.

return

ReturnNode

sclass

Singleton class declaration.

Two children. The first child is the expression for the class being opened (e.g. self); second child is a body statement.

class << some_var

SelfClassNode

self

Access to self

None

self

N/A

send

Non-safe method invocation (i.e. top-level or using a dot)

First child is the receiver node (e.g. self), second child is the method name (e.g. :foo=) and the remaining children (if any) are the arguments (expression nodes).

foo or foo.bar

SendNode

shadowarg

Shadow argument, aka block-local variable. Must come inside an args.

One child - a symbol, representing the argument name.

foo { |a; b| b }

ArgNode

splat

Array or function argument * operator

One child, an expression.

*foo

N/A

str

Non-interpolated string literal. The heredoc version works very differently from the regular version and the location info is totally separate.

One child, the String content.

"hi mom"

StrNode

super

Super method call with arguments and/or brackets.

Children are expression nodes representing arguments.

super(a, b, c)

SuperNode

sym

Non-interpolated symbol

One child, the Symbol content.

:foo

SymbolNode

true

True literal

None

true

N/A

undef

Method undefinition

A list of sym, or dsym nodes representing method names to undefine.

undef :foo, :bar

N/A

until

Negative loop with condition coming first.

Two children. First child is an expression node for condition, second child is a body statement.

until foo do bar; end

UntilNode

until_post

Negative loop with condition coming last.

Two children. First child is an expression node for condition, second child is a body statement.

begin; foo; end until condition

UntilNode

when

Case matching. Usually nested under case nodes.

Two children. First child is a regexp, expression node, or splat node for the condition. Second child is an expression node or begin node for the results.

when a then

WhenNode

while

Loop with condition coming first.

Two children. First child is an expression node for condition, second child is a body statement.

while foo do bar; end

WhileNode

while_post

Loop with condition coming last.

Two children. First child is an expression node for condition, second child is a body statement.

begin; foo; end while condition

WhileNode

xstr

Execute string (backticks). The heredoc version is treated totally differently from the regular version.

Children are split into str nodes, with interpolation represented by separate expression nodes .

`date`

StrNode

yield

Yield to a block.

Children are expression nodes representing arguments.

yield(foo)

YieldNode

zsuper

Super method call with no arguments or brackets.

None

super

SuperNode