RSpec matcher with block execution

custom_rspec_matcher_with_block.rb

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  gem "rspec"
end

require 'rspec/autorun'

RSpec.configure do |rspec|
  rspec.default_formatter = 'doc'
end

# https://twitter.com/kennethmayer/status/1283084667843776515
# Rspec Twitter: Is it possible to write a custom matcher that also yields to a given block?
RSpec.describe do
  RSpec::Matchers.define :match_to_string do |expected|
    match do |actual|
      match = true

      unless actual.to_s == expected.to_s
        @failure_message_expectation = "expected that #{actual}.to_s would be a eq to #{expected}.to_s. "
        match = false
      end

      unless @matcher_block.call(actual, expected)
        @failure_message = @failure_message_custom_matcher
        match = false
      end

      match
    end

    chain :and_call_custom_matcher do |custom_matcher|
      @failure_message_custom_matcher = custom_matcher.failure_message
      @matcher_block = custom_matcher.quick_matcher
    end

    failure_message do |actual|
      @failure_message_expectation.to_s + @failure_message.to_s
    end
  end

  Matcher = Struct.new(:quick_matcher, :failure_message)
  quick_matcher = ->(first_expect, second_expect) do
    first_expect.class == second_expect.class
  end
  matcher = Matcher.new(quick_matcher, "Class do not match")

  it 'no fail' do
    expect('u').to match_to_string('u').and_call_custom_matcher(matcher)
  end

  it 'with first failing matcher' do
    expect('u').to match_to_string('v').and_call_custom_matcher(matcher)
  end

  it 'with second failing matcher' do
    expect('u').to match_to_string(:u).and_call_custom_matcher(matcher)
  end

  it 'with both failing matchers' do
    expect('u').to match_to_string(:r).and_call_custom_matcher(matcher)
  end
end

Fetching gem metadata from https://rubygems.org/...
Resolving dependencies...
Using bundler 2.1.4
Using diff-lcs 1.4.4
Using rspec-support 3.9.3
Using rspec-core 3.9.2
Using rspec-expectations 3.9.2
Using rspec-mocks 3.9.1
Using rspec 3.9.0


  no fail
  with first failing matcher (FAILED - 1)
  with second failing matcher (FAILED - 2)
  with both failing matchers (FAILED - 3)

Failures:

  1) with first failing matcher
     Failure/Error: expect('u').to match_to_string('v').and_call_custom_matcher(matcher)
       expected that u.to_s would be a eq to v.to_s.
     # custom_matcher_yield.rb:61:in `block (2 levels) in <main>'

  2) with second failing matcher
     Failure/Error: expect('u').to match_to_string(:u).and_call_custom_matcher(matcher)
       Class do not match
     # custom_matcher_yield.rb:65:in `block (2 levels) in <main>'

  3) with both failing matchers
     Failure/Error: expect('u').to match_to_string(:r).and_call_custom_matcher(matcher)
       expected that u.to_s would be a eq to r.to_s. Class do not match
     # custom_matcher_yield.rb:69:in `block (2 levels) in <main>'

Finished in 0.01511 seconds (files took 0.07976 seconds to load)
4 examples, 3 failures

Failed examples:

rspec custom_matcher_yield.rb:60 # with first failing matcher
rspec custom_matcher_yield.rb:64 # with second failing matcher
rspec custom_matcher_yield.rb:68 # with both failing matchers