Initial topic for passing parameters by reference (#71)

resolves #39

Author: rwdougla

sources/modules/functions/passing-parameters-by-reference.md

@@ -0,0 +1,98 @@
+# Module name: Passing Parameters by Reference
+_Skeleton descriptions are typeset in italic text,_
+_so please don't remove these descriptions when editing the topic._
+
+## Overview
+
+_Provides a short natural language abstract of the module’s contents._
+_Specifies the different levels of teaching._
+
+<table>
+  <thead>
+    <th>Level</th>
+    <th>Objectives</th>
+  </thead>
+  <tr>
+    <td>Foundational</td>
+    <td>Avoiding copies using const-reference modifiers</td>
+  </tr>
+  <tr>
+    <td>Main</td>
+    <td>Using references to modify external data</td>
+  </tr>
+  <tr>
+    <td>Advanced</td>
+    <td></td>
+  </tr>
+</table>
+
+## Motivation
+
+_Why is this important?_
+_Why do we want to learn/teach this topic?_
+
+## Topic introduction
+
+_Very brief introduction to the topic._
+
+Explain what a reference type is and how it constrasts with a value type.
+
+## Foundational: Using reference types to avoid copies
+
+### Background/Required Knowledge
+
+A student is able to:
+
+* Define and call a function with parameters
+
+### Student outcomes
+
+_A list of things "a student should be able to" after the curriculum._
+_The next word should be an action word and testable in an exam._
+_Max 5 items._
+
+A student should be able to:
+
+1. Use const-refernce types for function arguments
+2. Explain what considerations to take when deciding whether or not to use a const-reference type
+
+### Caveats
+
+_This section mentions subtle points to understand, like anything resulting in
+implementation-defined, unspecified, or undefined behavior._
+
+### Points to cover
+
+_This section lists important details for each point._
+
+* No copy of the data is made when taken by constant reference
+* A constant reference value cannot be modified
+* The lifetime of a constant reference cannot be expected to extend beyond the lifetime of the function, so the reference should not be saved off for future use.
+* Taking a reference is not always a time or space savings. Modern machines may use 8-bytes to reference a 4-byte integer, for instance.
+
+## Main: Using references to modify external data 
+
+### Background/Required Knowledge
+
+* All of the above
+
+### Student outcomes
+
+A student should be able to:
+
+1. Define and utilize a non-const reference for passing values out of a function
+
+### Caveats
+
+### Points to cover
+
+* If the function does not intend to modify the value, const-references should be preferred
+* A reference value may be modified
+* The lifetime of a reference cannot be expected to extend beyond the lifetime of the function, so the reference should not be saved off for future use.
+* Taking a reference is not always a time or space savings. Modern machines may use 8-bytes to reference a 4-byte integer, for instance.
+
+## Advanced
+
+_These are important topics that are not expected to be covered but provide
+guidance where one can continue to investigate this topic in more depth._
+