Elaborate doc for attribute read and write methods [ci-skip]

This commit elaborates the documentation for the Active Record `#[]`,
`#[]=`, and `#read_attribute` methods, including adding pointers to
`ActiveModel::Type` for information about specific type casting
behavior.  In turn, this commit removes the note about casting empty
strings from the `#write_attribute` method.

activerecord/lib/active_record/attribute_methods.rb

@@ -310,36 +310,40 @@ def attribute_present?(attr_name)
       !value.nil? && !(value.respond_to?(:empty?) && value.empty?)
     end
 
-    # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
-    # "2004-12-12" in a date column is cast to a date object, like <tt>Date.new(2004, 12, 12)</tt>). It raises
-    # ActiveModel::MissingAttributeError if the identified attribute is missing.
-    #
-    # Note: +:id+ is always present.
+    # Returns the value of the attribute identified by +attr_name+ after it has
+    # been type cast. (For information about specific type casting behavior, see
+    # the types under ActiveModel::Type.)
     #
     #   class Person < ActiveRecord::Base
     #     belongs_to :organization
     #   end
     #
-    #   person = Person.new(name: 'Francesco', age: '22')
-    #   person[:name] # => "Francesco"
-    #   person[:age]  # => 22
+    #   person = Person.new(name: "Francesco", date_of_birth: "2004-12-12")
+    #   person[:name]            # => "Francesco"
+    #   person[:date_of_birth]   # => Date.new(2004, 12, 12)
+    #   person[:organization_id] # => nil
+    #
+    # Raises ActiveModel::MissingAttributeError if the attribute is missing.
+    # Note, however, that the +id+ attribute will never be considered missing.
     #
-    #   person = Person.select('id').first
-    #   person[:name]            # => ActiveModel::MissingAttributeError: missing attribute: name
+    #   person = Person.select(:name).first
+    #   person[:name]            # => "Francesco"
+    #   person[:date_of_birth]   # => ActiveModel::MissingAttributeError: missing attribute: date_of_birth
     #   person[:organization_id] # => ActiveModel::MissingAttributeError: missing attribute: organization_id
+    #   person[:id]              # => nil
     def [](attr_name)
       read_attribute(attr_name) { |n| missing_attribute(n, caller) }
     end
 
-    # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+.
+    # Updates the attribute identified by +attr_name+ using the specified
+    # +value+. The attribute value will be type cast upon being read.
     #
     #   class Person < ActiveRecord::Base
     #   end
     #
     #   person = Person.new
-    #   person[:age] = '22'
-    #   person[:age] # => 22
-    #   person[:age].class # => Integer
+    #   person[:date_of_birth] = "2004-12-12"
+    #   person[:date_of_birth] # => Date.new(2004, 12, 12)
     def []=(attr_name, value)
       write_attribute(attr_name, value)
     end

activerecord/lib/active_record/attribute_methods/read.rb

@@ -21,9 +21,10 @@ def define_method_attribute(name, owner:)
           end
       end
 
-      # Returns the value of the attribute identified by <tt>attr_name</tt> after
-      # it has been typecast (for example, "2004-12-12" in a date column is cast
-      # to a date object, like <tt>Date.new(2004, 12, 12)</tt>).
+      # Returns the value of the attribute identified by +attr_name+ after it
+      # has been type cast. For example, a date attribute will cast "2004-12-12"
+      # to <tt>Date.new(2004, 12, 12)</tt>. (For information about specific type
+      # casting behavior, see the types under ActiveModel::Type.)
       def read_attribute(attr_name, &block)
         name = attr_name.to_s
         name = self.class.attribute_aliases[name] || name

activerecord/lib/active_record/attribute_methods/write.rb

@@ -25,9 +25,8 @@ def define_method_attribute=(name, owner:)
           end
       end
 
-      # Updates the attribute identified by <tt>attr_name</tt> with the
-      # specified +value+. Empty strings for Integer and Float columns are
-      # turned into +nil+.
+      # Updates the attribute identified by +attr_name+ using the specified
+      # +value+. The attribute value will be type cast upon being read.
       def write_attribute(attr_name, value)
         name = attr_name.to_s
         name = self.class.attribute_aliases[name] || name