class RubbyCop::NodePattern
This class performs a pattern-matching operation on an AST
node.
Initialize a new `NodePattern` with `NodePattern.new(pattern_string)`, then pass an AST
node to `NodePattern#match`. Alternatively, use one of the class macros in `NodePattern::Macros` to define your own pattern-matching method.
If the match fails, `nil` will be returned. If the match succeeds, the return value depends on whether a block was provided to `#match`, and whether the pattern contained any “captures” (values which are extracted from a matching AST
.)
-
With block: match yields the captures (if any) and passes the return
value of the block through.
-
With no block, but one capture: the capture is returned.
-
With no block, but multiple captures: captures are returned as an array.
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With no block and no captures: match returns `true`.
## Pattern string format examples
':sym' # matches a literal symbol '1' # matches a literal integer 'nil' # matches a literal nil 'send' # matches (send ...) '(send)' # matches (send) '(send ...)' # matches (send ...) '(op-asgn)' # node types with hyphenated names also work '{send class}' # matches (send ...) or (class ...) '({send class})' # matches (send) or (class) '(send const)' # matches (send (const ...)) '(send _ :new)' # matches (send <anything> :new) '(send $_ :new)' # as above, but whatever matches the $_ is captured '(send $_ $_)' # you can use as many captures as you want '(send !const ...)' # ! negates the next part of the pattern '$(send const ...)' # arbitrary matching can be performed on a capture '(send _recv _msg)' # wildcards can be named (for readability) '(send ... :new)' # you can specifically match against the last child # (this only works for the very last) '(send $...)' # capture all the children as an array '(send $... int)' # capture all children but the last as an array '(send _x :+ _x)' # unification is performed on named wildcards # (like Prolog variables...) # (#== is used to see if values unify) '(int odd?)' # words which end with a ? are predicate methods, # are are called on the target to see if it matches # any Ruby method which the matched object supports # can be used # if a truthy value is returned, the match succeeds '(int [!1 !2])' # [] contains multiple patterns, ALL of which must # match in that position # in other words, while {} is pattern union (logical # OR), [] is intersection (logical AND) '(send %1 _)' # % stands for a parameter which must be supplied to # #match at matching time # it will be compared to the corresponding value in # the AST using #== # a bare '%' is the same as '%1' # the number of extra parameters passed to #match # must equal the highest % value in the pattern # for consistency, %0 is the 'root node' which is # passed as the 1st argument to #match, where the # matching process starts '^^send' # each ^ ascends one level in the AST # so this matches against the grandparent node '#method' # we call this a 'funcall'; it calls a method in the # context where a pattern-matching method is defined # if that returns a truthy value, the match succeeds 'equal?(%1)' # predicates can be given 1 or more extra args '#method(%0, 1)' # funcalls can also be given 1 or more extra args
You can nest arbitrarily deep:
# matches node parsed from 'Const = Class.new' or 'Const = Module.new': '(casgn nil const (send (const nil {:Class :Module}) :new)))' # matches a node parsed from an 'if', with a '==' comparison, # and no 'else' branch: '(if (send _ :== _) _ nil)'
Note that patterns like 'send' are implemented by calling `#send_type?` on the node being matched, 'const' by `#const_type?`, 'int' by `#int_type?`, and so on. Therefore, if you add methods which are named like `#prefix_type?` to the AST
node class, then 'prefix' will become usable as a pattern.
Also note that if you need a “guard clause” to protect against possible nils in a certain place in the AST
, you can do it like this: `[!nil <pattern>]`
The compiler code is very simple; don't be afraid to read through it!
Constants
- Invalid
@private
Public Class Methods
# File lib/rubbycop/node_pattern.rb, line 536 def initialize(str) compiler = Compiler.new(str) src = "def match(node0#{compiler.emit_trailing_params});" \ "#{compiler.emit_method_code}end" instance_eval(src) end