From 3057f66e667414d653b5a8381f2a6ced81e8c10a Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Thu, 21 Sep 2017 23:05:48 -0700
Subject: [PATCH] Throw the exception instead of returning null.

---
 .../abacus/exception/ContextException.java    | 24 +++++++++++++++++++
 .../abacus/context/ChainSearchDelegate.kt     |  7 +++---
 .../nwapw/abacus/context/EvaluationContext.kt |  6 ++---
 3 files changed, 31 insertions(+), 6 deletions(-)
 create mode 100644 core/src/main/java/org/nwapw/abacus/exception/ContextException.java

diff --git a/core/src/main/java/org/nwapw/abacus/exception/ContextException.java b/core/src/main/java/org/nwapw/abacus/exception/ContextException.java
new file mode 100644
index 0000000..dd2db0e
--- /dev/null
+++ b/core/src/main/java/org/nwapw/abacus/exception/ContextException.java
@@ -0,0 +1,24 @@
+package org.nwapw.abacus.exception;
+
+/**
+ * Exception thrown by the Context in cases where lookup fails
+ * where it should not.
+ */
+public class ContextException extends AbacusException {
+
+    /**
+     * Creates a new ContextException without an extra message.
+     */
+    public ContextException() {
+        this("");
+    }
+
+    /**
+     * Creates a ContextException with the given message.
+     * @param message the message to use.
+     */
+    public ContextException(String message){
+        super("Context exception", message);
+    }
+
+}
diff --git a/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt b/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt
index b1245b9..64d933a 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt
@@ -1,5 +1,6 @@
 package org.nwapw.abacus.context
 
+import org.nwapw.abacus.exception.ContextException
 import kotlin.reflect.KProperty
 
 /**
@@ -16,14 +17,14 @@ import kotlin.reflect.KProperty
  */
 class ChainSearchDelegate<out V>(private val valueGetter: EvaluationContext.() -> V?) {
 
-    operator fun getValue(selfRef: Any, property: KProperty<*>): V? {
-        var currentRef = selfRef as? EvaluationContext ?: return null
+    operator fun getValue(selfRef: Any, property: KProperty<*>): V {
+        var currentRef = selfRef as EvaluationContext
         var returnedValue = currentRef.valueGetter()
         while (returnedValue == null) {
             currentRef = currentRef.parent ?: break
             returnedValue = currentRef.valueGetter()
         }
-        return returnedValue
+        return returnedValue ?: throw ContextException()
     }
 
 }
\ No newline at end of file
diff --git a/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt b/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt
index d4fdadd..293a5ff 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt
@@ -43,13 +43,13 @@ open class EvaluationContext(val parent: EvaluationContext? = null,
     /**
      * The implementation inherited from this context's parent.
      */
-    val inheritedNumberImplementation: NumberImplementation?
-            by ChainSearchDelegate { numberImplementation}
+    val inheritedNumberImplementation: NumberImplementation
+            by ChainSearchDelegate { numberImplementation }
 
     /**
      * The reducer inherited from this context's parent.
      */
-    val inheritedReducer: Reducer<NumberInterface>?
+    val inheritedReducer: Reducer<NumberInterface>
             by ChainSearchDelegate { reducer }
 
     /**