Default Parameters (#56)

Integrates initial work on default parameters.

Author: rwdougla

functions/calling-functions.md

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+# C++ functions: calling functions
+
+This topic is currently under construction and will soon be filled with information :)

functions/defaulted-parameters.md

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+# Functions: default argument
+_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 arguments for some number 
+of parameters, to allow a caller to avoid specifying arguments that 
+rarely change, or to enable expanding the set of parameters while 
+maintaining backward compatibility with existing callers.
+
+<table>
+  <thead>
+    <th>Level</th>
+    <th>Objectives</th>
+  </thead>
+  <tr>
+    <td>Foundational</td>
+    <td>Define and use functions with default arguments</td>
+  </tr>
+  <tr>
+    <td>Main</td>
+    <td></td>
+  </tr>
+  <tr>
+    <td>Advanced</td>
+    <td>refinement of default arguments through multiple declarations</td>
+  </tr>
+</table>
+
+## Motivation
+
+Default arguments allow the omission of arguments with obvious or common
+values. Also may be utilized to extend an existing function signature 
+without forcing changes to existing calling code.
+
+## Topic introduction
+
+Explain how default arguments work and how to define them.
+
+## Foundational: Using and defining functions with default arguments
+
+### Background/Required Knowledge
+
+A student is able to:
+
+* Make calls to existing functions, passing arguments [[Functions: calling functions]][1]
+* Declare member and non-member functions, separate from definitions
+* Define member and non-member functions [[Functions: member functions]][2]
+* Explain what a default constructor is and does [[C++ object model: constructors]][3]
+
+### Student outcomes
+
+A student should be able to:
+
+1. Call to a function with a default argument with or without that argument specified
+2. Declare a function with a default argument, and omit the default in the definition's signature
+3. Explain when the lifetime of a default argument begins and ends
+
+
+### Caveats
+
+* 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.
+* Additional default values may be specified for other parameters in repeat declarations
+* Calling an overloaded function with fewer arguments may be ambiguous with regard to an overload with default arguments
+
+### Points to cover
+
+* Default value may only be specified once for each parameter among all declarations
+* Default values must start from the rightmost parameter and continue leftward without gaps
+* Considerations of when to use default arguments vs overload set
+
+## Main: implementing *
+
+### Background/required knowledge
+
+* All of the above.
+
+### Student outcomes
+
+A student should be able to:
+
+### Caveats
+
+
+### Points to cover
+
+## Advanced
+
+Subsequent redeclarations of the same function may add default argument
+values, which are then usable by callers.
+Though a single parameter cannot be given a default argument twice in the same 
+translation unit, it is legal, though ill-advised, to give the same
+function different default arguments in different translation units.
+
+
+[1]: ../functions/calling-functions.md
+[2]: ../functions/member-functions.md
+[3]: ../object-model/constructors.md

functions/member-functions.md

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+# C++ functions: member functions
+
+This topic is currently under construction and will soon be filled with information :)

object-model/constructors.md

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+# C++ object model: constructor
+
+This topic is currently under construction and will soon be filled with information :)