Source tree substitution examples

substitution_example.rb

# Example 1: Swap the consequence and else statements in an if expression

if_node = CodeMiner.parse(<<-RUBY).each.first
if foo
  begin
    do_something
  end
else
  do_something_else
end
RUBY

swap_consequence_with_else = CodeMiner::Substitution::Value.new(if_node.consequence, if_node.else_statement.body.src)
swap_else_with_consequence = CodeMiner::Substitution::Value.new(if_node.else_statement.body, if_node.consequence.src)
puts CodeMiner::Substitution.new(if_node).substitute(swap_consequence_with_else, swap_else_with_consequence)

=begin output

if foo
  do_something_else
else
  begin
    do_something
  end
end

=end

# Example 2: Convert a transformation that mutates an external array into a call to map

iter_node = CodeMiner.parse(<<-RUBY).each.first
foo.each do |i|
  array << process(i)
end
RUBY

array_mutation = iter_node.block.body.each.first

each_to_map = CodeMiner::Substitution::Value.new(iter_node.token, 'map')
unwrap_transformation = CodeMiner::Substitution::Value.new(array_mutation, array_mutation.body.src)

puts CodeMiner::Substitution.new(iter_node).substitute(each_to_map, unwrap_transformation)

=begin output

foo.map do |i|
  process(i)
end

=end

# Example 3: Convert a filter that mutates an external array into a call to select

iter_node = CodeMiner.parse(<<-RUBY).each.first
foo.each do |i|
  if i % 2 == 0
    array << i
  end
end
RUBY

if_node = iter_node.block.body.each.first
array_mutation = if_node.consequence.body.each.first

each_to_select = CodeMiner::Substitution::Value.new(iter_node.token, 'select')
unwrap_conditional_test = CodeMiner::Substitution::Value.new(if_node, if_node.test.src)

puts CodeMiner::Substitution.new(iter_node).substitute(each_to_select, unwrap_conditional_test)

=begin output

foo.select do |i|
  i % 2 == 0
end

=end