Add Transfrom to support functional mapping

README.md

@@ -220,6 +220,11 @@ Collection picked = Collection.of(opportunities).pick(new Set<String>{'Name', 'A
 
 Maps all elements of `Collection` view into another `Collection` view with the provided `SObjectToSObjectFunction` mapping function.
 
+| Modifier and type | Method | Description |
+|-------------------|--------|-------------|
+| `Collection` | `mapAll(SObjectToSObjectFunction fn)` | Returns a new `Collection` view formed by mapping all current view elements with `fn` |
+
+
 ```apex
 private class DoubleAmount implements SObjectToSObjectFunction {
     public SObject apply(SObject record) {
@@ -236,9 +241,16 @@ List<Opportunity> opps = new List<Opportunity>{
 Collection.of(opps).mapAll(new DoubleAmount()); // amounts have been doubled
 ```
 
-| Modifier and type | Method | Description |
-|-------------------|--------|-------------|
-| `Collection` | `mapAll(SObjectToSObjectFunction fn)` | Returns a new `Collection` view formed by mapping all current view elements with `fn` |
+One `SObjectToSObjectFunction` is provided out of the box, `RecordTransform`. It is instantiated through a factory method on `Transform`:
+
+#### `RecordTransform`
+
+`RecordTransform` copies all defined fields from `prototype` record to the record it is applied to. Values of fields defined for `prototype` are overwritten on
+target records. Other fields on target record are not modified.
+
+```apex
+Collection.of(opps).mapAll(Transform.record(new Opportunity(Name = 'Test'))); // Name field has been overwritten with 'Test'
+```
 
 ### `mapSome`
 <a name="map-some"></a>

src/classes/CollectionTest.cls

@@ -458,4 +458,14 @@ public class CollectionTest {
 		System.assertEquals(200, opportunities[0].Amount);
 		System.assertEquals(150, opportunities[1].Amount);
 	}
+
+	@IsTest
+	static void testMapWithTransform() {
+		List<Opportunity> opportunities = Collection.of(new List<Opportunity>{
+			new Opportunity(Amount = 100),
+			new Opportunity(Amount = 150)
+		}).mapAll(Transform.record(new Opportunity(Amount = 123))).asList();
+		System.assertEquals(123, opportunities[0].Amount);
+		System.assertEquals(123, opportunities[1].Amount);
+	}
 }

src/classes/RecordTransform.cls

@@ -0,0 +1,17 @@
+public class RecordTransform implements SObjectToSObjectFunction {
+	private SObject prototype;
+	private Map<String, Object> populatedFieldsMap;
+
+	public SObject apply(SObject record) {
+
+		for (String field : populatedFieldsMap.keySet()) {
+			record.put(field, prototype.get(field));
+		}
+		return record;
+	}
+
+	public RecordTransform(sObject prototype) {
+		this.prototype = prototype;
+		this.populatedFieldsMap = prototype.getPopulatedFieldsAsMap();
+	}
+}

src/classes/RecordTransform.cls-meta.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
+    <apiVersion>44.0</apiVersion>
+    <status>Active</status>
+</ApexClass>

src/classes/RecordTransformTest.cls

@@ -0,0 +1,19 @@
+@IsTest
+public class RecordTransformTest {
+	@IsTest
+	public static void definedFieldsAreUsed() {
+		Opportunity opp = new Opportunity();
+		RecordTransform t = Transform.record(new Opportunity(Amount = 1000, Name = 'Test'));
+		t.apply(opp);
+		System.assertEquals(1000, opp.Amount);
+		System.assertEquals('Test', opp.Name);
+	}
+
+	@IsTest
+	public static void fieldsAreOverwritten() {
+		Opportunity opp = new Opportunity(Amount = 1000);
+		RecordTransform t = Transform.record(new Opportunity(Amount = 2000));
+		t.apply(opp);
+		System.assertEquals(2000, opp.Amount);
+	}
+}

src/classes/RecordTransformTest.cls-meta.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
+    <apiVersion>44.0</apiVersion>
+    <status>Active</status>
+</ApexClass>

src/classes/Transform.cls

@@ -0,0 +1,5 @@
+public with sharing class Transform {
+	public static RecordTransform record(SObject record) {
+		return new RecordTransform(record);
+	}
+}

src/classes/Transform.cls-meta.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
+    <apiVersion>44.0</apiVersion>
+    <status>Active</status>
+</ApexClass>