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@estum
Last active August 8, 2023 05:52
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Ruby alternative switch-case syntax.
# = Kernel#switch
# Provides alternative switch-case syntax.
#
# # support methods:
# value = []
# switch value do
# on empty?: -> { "none" }
# on one?: -> { "one" }
# on many?: -> { "many" }
# end
#
# # More:
# switch value do
# on Hash => proc { value }
# on Array => lambda { Hash[value] }
# on Post, Comment do
# value.as_json
# end
# default { fail "¯\_(ツ)_/¯" }
# end
#
# # ...and more:
# value = "false"
# switch value do
# on /^(\d+)$/, ->{ Regexp.last_matches[1].to_i } # Sorry, no $N-vars :'(
# on /^(\d+\.?\d*)$/, ->{ value.to_f }
# on /^true|false$/i, ->{ value =~ "true" }
# default { value }
# end
class SwitchOn
class MultipleDefaultCaseError < SyntaxError; end
class MissingStatementBlockError < SyntaxError; end
class Case
def initialize(*args, &block)
if block_given?
proc = block.to_proc
else
if args.one? && args[0].is_a?(Hash)
*args, proc = args[0].to_a[0]
elsif args.many?
proc = args.pop
end
end
raise MissingStatementBlockError unless proc.is_a? Proc
@matches, @proc = args, proc
end
def call
@proc.call
end
def match?(object)
@matches.each {|m| break true if perform_match(object, m) } === true
end
private
def perform_match(object, match)
return method_match(object, match) if match.is_a?(Symbol) && object.respond_to?(match)
match === object
end
def method_match(object, match)
result = object.send(match) rescue nil
[true, false].include?(result) ? result : (match === object)
end
end
def initialize(&block)
@cases = []
@found = false
instance_eval(&block)
end
def on(*args, &block)
@cases << Case.new(*args, &block)
end
def default(&block)
raise MultipleDefaultCaseError unless @default.nil?
@default = block.to_proc
end
def call(object)
result = @cases.each do |kase|
found! if kase.match? object
break kase.call if found?
end
found? ? result : default_or_nil
end
private
def default_or_nil
@default.call if @default.is_a? Proc
end
def found!
@found = true
end
def found?
@found === true
end
end
module Kernel
def switch(object, &block)
SwitchOn.new(&block).call(object)
end
end
@focused
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focused commented Aug 26, 2016

Nice, similar to pattern matching

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