Allow set to take a lambda

docs/pre_processing_fields.md

@@ -24,6 +24,15 @@ Set a field to a given value.
   end
 ```
 
+The field may be set to the return value of a lambda, so to set a field to the
+current time:
+
+```ruby
+  amoeba do
+    set datetime_field: ->() { Time.now }
+  end
+```
+
 ## regex
 
 To do

lib/amoeba/cloner.rb

@@ -135,7 +135,7 @@ def process_null_fields
     def process_coercions
       # prepend any extra strings to indicate uniqueness of the new record(s)
       amoeba.coercions.each do |field, coercion|
-        @new_object[field] = coercion.to_s
+        @new_object[field] = coercion.is_a?(Proc) ? coercion.call : coercion.to_s
       end
     end
 

spec/lib/amoeba/class_methods_spec.rb

@@ -62,6 +62,23 @@
 
         it { expect(dup.test_field).to be(false) }
       end
+
+      context 'with a datetime field set by a lambda' do
+        let(:params) { { test_field: DateTime.parse('30 Jun 2024 18:19') } }
+        let(:field_type) { :datetime }
+        let(:config) do
+          <<~CONFIG
+            amoeba do
+              set test_field: ->() { Time.now }
+            end
+          CONFIG
+        end
+
+        before { travel_to DateTime.parse('1 Jul 2024 09:35') }
+        after { travel_back }
+
+        it { expect(dup.test_field).to eq(DateTime.parse('1 Jul 2024 09:35')) }
+      end
     end
   end
 end

spec/spec_helper.rb

@@ -19,6 +19,7 @@
 end
 
 require 'active_record'
+require 'active_support/testing/time_helpers'
 require 'amoeba'
 
 adapter = if defined?(JRuby)
@@ -32,6 +33,7 @@
 ActiveRecord::Base.establish_connection(adapter: adapter, database: ':memory:')
 
 ::RSpec.configure do |config|
+  config.include ActiveSupport::Testing::TimeHelpers
   config.order = :defined
 end