Default Parameters

Issue cplusplus#40

functions/defaulted_parameters.md

@@ -0,0 +1,89 @@
+# Module name: topic name
+_Skeleton instructions are typeset in italic text._
+
+## Overview
+
+Functions in C++ may be overloaded with different numbers and types of parameters. It may be of value to specify default values for some number of parameters, to allow a consumer to avoid specifying parameters that rarely change, or to enable expanding the set of parameters while maintaining backward compatibility with existing consumers.
+
+<table>
+  <thead>
+    <th>Level</th>
+    <th>Objectives</th>
+  </thead>
+  <tr>
+    <td>Foundational knowledge</td>
+    <td>can make calls to functions with defaulted parameters, with or without defaulted parameters</td>
+  </tr>
+  <tr>
+    <td>Advanced</td>
+    <td>declares and defines functions with defaulted parameters</td>
+  </tr>
+  <tr>
+    <td>Further studies</td>
+    <td>refinement of defaulted parameters through multiple declarations</td>
+  </tr>
+</table>
+
+## Motivation
+
+Default parameters allow the omission of explicitly stating commonly defined parameters, using sensible defaults. Also allows expansion of function signature without forcing existing consumers to modify their calls.
+
+## Topic introduction
+
+Explains how default parameters work and how to define them.
+
+## Foundational knowledge: Using *
+
+### Background/Required Knowledge
+
+A student is able to:
+
+* Make calls existing functions using parameters
+* Declare member and non-member functions, separate from definitions
+* Define member and non-member functions
+* Explain what a default constructor is and does
+
+### Student outcomes
+
+A student should be able to:
+
+1. Call to a function with a default parameter with or without that parameter specified
+2. Explain what the requirements are for a type to be usable with a default parameter
+
+### Caveats
+
+_This section mentions subtle points to understand, like anything resulting in
+implementation-defined, unspecified, or undefined behavior._
+
+* When no forward-declaration exists, the definition serves as the declaration
+* When multiple declarations exist, only one may specify the default for any particular parameter, but multiple declarations may specify the defaults for different parameters.
+* Default values may be specified for new parameters in new declarations
+* Calling an overloaded function with fewer parameters may be ambiguous with regard to an overload with defaulted parameters
+
+### Points to cover
+
+_This section lists important details for each point._
+
+* Default value may only be specified once for each parameter
+* Default values must start from the right
+
+## Advanced: implementing *
+
+### Background/required knowledge
+
+* All of the above.
+
+### Student outcomes
+
+A student should be able to:
+
+1. Declare a function with a default parameter, and omit the default in the definition's signature
+
+### Caveats
+
+### Points to cover
+
+## Further studies
+
+_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._