Merge pull request #26 from Jack-Edwards/try-from

Implement validation without throwing exceptions

ValueOf.Tests/TryValidate.cs

@@ -0,0 +1,34 @@
+using NUnit.Framework;
+
+namespace ValueOf.Tests
+{
+    public class TryValidateClientRef : ValueOf<string, TryValidateClientRef>
+    {
+        protected override bool TryValidate()
+        {
+            return !string.IsNullOrWhiteSpace(Value);
+        }
+    }
+
+    public class TryValidation
+    {
+        [Test]
+        public void TryValidateReturnsFalse()
+        {
+            bool isValid = TryValidateClientRef.TryFrom("", out TryValidateClientRef valueObject);
+
+            Assert.IsFalse(isValid);
+            Assert.IsNull(valueObject);
+        }
+
+        [Test]
+        public void TryValidateReturnsTrue()
+        {
+            bool isValid = TryValidateClientRef.TryFrom("something", out TryValidateClientRef valueObject);
+
+            Assert.IsTrue(isValid);
+            Assert.IsNotNull(valueObject);
+            Assert.AreEqual("something", valueObject.Value);
+        }
+    }
+}

ValueOf/ValueOf.cs

@@ -20,6 +20,11 @@ protected virtual void Validate()
         {
         }
 
+        protected virtual bool TryValidate()
+        {
+            return true;
+        }
+
         static ValueOf()
         {
             ConstructorInfo ctor = typeof(TThis)
@@ -45,6 +50,18 @@ public static TThis From(TValue item)
             return x;
         }
 
+        public static bool TryFrom(TValue item, out TThis thisValue)
+        {
+            TThis x = Factory();
+            x.Value = item;
+
+            thisValue = x.TryValidate()
+               ? x
+               : null;
+
+            return thisValue != null;
+        }
+
         protected virtual bool Equals(ValueOf<TValue, TThis> other)
         {
             return EqualityComparer<TValue>.Default.Equals(Value, other.Value);