Calculate the minimum/maximum from an enumerable's extracted elements

```
payments = [Payment.new(5), Payment.new(15), Payment.new(10)]
payments.minimum(:price) # => 5
payments.maximum(:price) # => 20
```

actionpack/test/controller/render_test.rb

@@ -100,6 +100,15 @@ class TestController < ActionController::Base
     end
   end
 
+  def conditional_hello_with_array_of_records
+    record = Struct.new(:updated_at, :cache_key).new(Time.now.utc.beginning_of_day, "foo/123")
+    old_record = Struct.new(:updated_at, :cache_key).new(Time.now.utc.beginning_of_day.yesterday, "bar/123")
+
+    if stale?([record, old_record])
+      render action: "hello_world"
+    end
+  end
+
   def dynamic_render
     render params[:id] # => String, AC::Params
   end
@@ -522,6 +531,34 @@ class LastModifiedRenderTest < ActionController::TestCase
     assert_equal @last_modified, @response.headers["Last-Modified"]
   end
 
+  def test_responds_with_last_modified_with_array_of_records
+    get :conditional_hello_with_array_of_records
+    assert_equal @last_modified, @response.headers["Last-Modified"]
+  end
+
+  def test_request_not_modified_with_array_of_records
+    @request.if_modified_since = @last_modified
+    get :conditional_hello_with_array_of_records
+    assert_equal 304, @response.status.to_i
+    assert_predicate @response.body, :blank?
+    assert_equal @last_modified, @response.headers["Last-Modified"]
+  end
+
+  def test_request_not_modified_but_etag_differs_with_array_of_records
+    @request.if_modified_since = @last_modified
+    @request.if_none_match = '"234"'
+    get :conditional_hello_with_array_of_records
+    assert_response :success
+  end
+
+  def test_request_modified_with_array_of_records
+    @request.if_modified_since = "Thu, 16 Jul 2008 00:00:00 GMT"
+    get :conditional_hello_with_array_of_records
+    assert_equal 200, @response.status.to_i
+    assert_predicate @response.body, :present?
+    assert_equal @last_modified, @response.headers["Last-Modified"]
+  end
+
   def test_responds_with_last_modified_with_collection_of_records
     get :conditional_hello_with_collection_of_records
     assert_equal @last_modified, @response.headers["Last-Modified"]

activesupport/CHANGELOG.md

@@ -1,3 +1,18 @@
+*   Add `Enumerable#maximum` and `Enumerable#minimum` to easily calculate the maximum or minimum from extracted
+    elements of an enumerable.
+
+    ```ruby
+    payments = [Payment.new(5), Payment.new(15), Payment.new(10)]
+
+    payments.minimum(:price) # => 5
+    payments.maximum(:price) # => 20
+    ```
+
+    This also allows passing enumerables to `fresh_when` and `stale?` in Action Controller.
+    See PR [#41404](https://github.com/rails/rails/pull/41404) for an example.
+
+    *Ayrton De Craene*
+
 *   `ActiveSupport::Cache::MemCacheStore` now accepts an explicit `nil` for its `addresses` argument.
 
     ```ruby

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -16,6 +16,22 @@ module Enumerable
 
   # :startdoc:
 
+  # Calculates the minimum from the extracted elements.
+  #
+  # payments = [Payment.new(5), Payment.new(15), Payment.new(10)]
+  # payments.minimum(:price) # => 5
+  def minimum(key)
+    map(&key).min
+  end
+
+  # Calculates the maximum from the extracted elements.
+  #
+  # payments = [Payment.new(5), Payment.new(15), Payment.new(10)]
+  # payments.maximum(:price) # => 15
+  def maximum(key)
+    map(&key).max
+  end
+
   # Calculates a sum from the elements.
   #
   #  payments.sum { |p| p.price * p.tax_rate }

activesupport/test/core_ext/enumerable_test.rb

@@ -29,6 +29,16 @@ class EnumerableTests < ActiveSupport::TestCase
     assert_equal(e, v, msg)
   end
 
+  def test_minimum
+    payments = GenericEnumerable.new([ Payment.new(5), Payment.new(15), Payment.new(10) ])
+    assert_equal 5, payments.minimum(:price)
+  end
+
+  def test_maximum
+    payments = GenericEnumerable.new([ Payment.new(5), Payment.new(15), Payment.new(10) ])
+    assert_equal 15, payments.maximum(:price)
+  end
+
   def test_sums
     enum = GenericEnumerable.new([5, 15, 10])
     assert_equal 30, enum.sum