Tools: Ruby Parser Designing and Maintaining Software (DAMS) Louis Rose
Parsing recapped Parsing (strictly speaking “lex-ing and parsing”) produces an intermediate representation of a program, called an AST.
ASTs recapped ASTs are tree data structures that can be analysed for meaning (following JLJ in SYAC 2014/15).
if
send
nil
:weekend?
send
nil
:snooze
send
nil
:get_up
if weekend? snooze else get_up end
There are many ways to Ruby Many Ruby constructs can be written with more than one concrete syntax. This does not change the abstract syntax.
if
send
nil
:weekend?
send
nil
:snooze
send
nil
:get_up
weekend? ? snooze : get_up
Why do we care about parsing? Many of the habitability factors can be approximated by using measurements of the AST. Leaner
Avoids Duplication
Less Complex
Clearer
Loosely Coupled
More Extensible
More Cohesive
???
Ruby’s parser gem A Ruby implementation of a Ruby parser. Can be used to parse Ruby on the command line: % gem install parser ... 2 gems installed % ruby-parse -e "if weekend? then snooze else get_up end” (if (send nil :weekend?) (send nil :snooze) (send nil :get_up)) % ruby-parse fake.rb (begin (send nil :require (str "faker")) (send nil :puts (send (const (const nil :Faker) :Name) :name))
Ruby’s parser gem Can also be used as a library from within our Ruby programs, which we’ll use heavily later in DAMS. require "parser/current" parser = Parser::CurrentRuby ast = parser.parse("weekend? ? snooze : get_up") ast.type # => :if ast.children.first.type # => :send ast.children.first.children[0] # => nil ast.children.first.children[1] # => :weekend?
Ruby’s parser gem Includes an abstract class for querying / rewriting the AST. require "parser/current" class SendCounter < Parser::AST::Processor attr_reader :total def initialize @total = 0 end def on_send(node) super(node) @total += 1 end end parser = Parser::CurrentRuby ast = parser.parse("weekend? ? snooze : get_up") counter = SendCounter.new counter.process(ast) counter.total # => 3
Designing and Maintaining Software (DAMS) - GitHub
ASTs are tree data structures that can be analysed for meaning (following JLJ in SYAC 2014/15) ... More Cohesive. Avoids Duplication. Clearer. More Extensible.
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Automatically detect similar fragments of code. class StuffedCrust def title. "Stuffed Crust " +. @toppings.title +. " Pizza" end def cost. @toppings.cost + 6 end end class DeepPan def title. "Deep Pan " +. @ingredients.title +. " Pizza" end def cost
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Coupling Between Objects. Counts the number of other classes to which a class is coupled (other than via inheritance). CBO(c) = |d â C - (1cl U Ancestors(C))| uses(c, d) V uses(d, c). - Chidamber and Kemerer. A metrics suite for object-oriented des
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When we are testing the way that a unit behaves when a condition is met, use a stub to setup the condition. Solution: use stubs for queries class Subscription ... def bill(amount) unless payments.exists(subscription_id: id) payments.charge(subscripti
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