Class | AST::Node |
In: |
lib/ast/node.rb
|
Parent: | Object |
Node is an immutable class, instances of which represent abstract syntax tree nodes. It combines semantic information (i.e. anything that affects the algorithmic properties of a program) with meta-information (line numbers or compiler intermediates).
Notes on inheritance
The distinction between semantics and metadata is important. Complete semantic information should be contained within just the {type} and {children} of a Node instance; in other words, if an AST was to be stripped of all meta-information, it should remain a valid AST which could be successfully processed to yield a result with the same algorithmic properties.
Thus, Node should never be inherited in order to define methods which affect or return semantic information, such as getters for `class_name`, `superclass` and `body` in the case of a hypothetical `ClassNode`. The correct solution is to use a generic Node with a {type} of `:class` and three children. See also {Processor} for tips on working with such ASTs.
On the other hand, Node can and should be inherited to define application-specific metadata (see also {initialize}) or customize the printing format. It is expected that an application would have one or two such classes and use them across the entire codebase.
The rationale for this pattern is extensibility and maintainability. Unlike static ones, dynamic languages do not require the presence of a predefined, rigid structure, nor does it improve dispatch efficiency, and while such a structure can certainly be defined, it does not add any value but incurs a maintaining cost. For example, extending the AST even with a transformation-local temporary node type requires making globally visible changes to the codebase.
children | -> | to_a |
dup | -> | original_dup |
children | [R] |
Returns the children of this node. The returned value is frozen. The to_a
alias is useful for decomposing nodes concisely. For example:
node = s(:gasgn, :$foo, s(:integer, 1)) var_name, value = *node p var_name # => :$foo p value # => (integer 1) @return [Array] |
hash | [R] | Returns the precomputed hash value for this node @return [Fixnum] |
type | [R] | Returns the type of this node. @return [Symbol] |
Constructs a new instance of Node.
The arguments `type` and `children` are converted with `to_sym` and `to_a` respectively. Additionally, the result of converting `children` is frozen. While mutating the arguments is generally considered harmful, the most common case is to pass an array literal to the constructor. If your code does not expect the argument to be frozen, use `dup`.
The `properties` hash is passed to {assign_properties}.
Compares `self` to `other`, possibly converting with `to_ast`. Only `type` and `children` are compared; metadata is deliberately ignored.
@return [Boolean]
Concatenates `array` with `children` and returns the resulting node.
@return [AST::Node]
Nodes are already frozen, so there is no harm in returning the current node as opposed to initializing from scratch and freezing another one.
@return self
Converts `self` to a s-expression ruby string. The code return will recreate the node, using the sexp module s()
@param [Integer] indent Base indentation level. @return [String]
Converts `self` to a pretty-printed s-expression.
@param [Integer] indent Base indentation level. @return [String]
Converts `self` to an Array where the first element is the type as a Symbol, and subsequent elements are the same representation of its children.
@return [Array<Symbol, […Array]>]
Returns a new instance of Node where non-nil arguments replace the corresponding fields of `self`.
For example, `Node.new(:foo, [ 1, 2 ]).updated(:bar)` would yield `(bar 1 2)`, and `Node.new(:foo, [ 1, 2 ]).updated(nil, [])` would yield `(foo)`.
If the resulting node would be identical to `self`, does nothing.
@param [Symbol, nil] type @param [Array, nil] children @param [Hash, nil] properties @return [AST::Node]
By default, each entry in the `properties` hash is assigned to an instance variable in this instance of Node. A subclass should define attribute readers for such variables. The values passed in the hash are not frozen or whitelisted; such behavior can also be implemented by subclassing Node and overriding this method.
@return [nil]