Free Functions

A function that is not a member of a class

• Useful for algorithms performed on the parameters
• All IN data is from a value or const reference parameter
• All OUT data is from a reference parameter or the return value
• Does not save state between calls
• Typically group (or organized) by file, e.g., xml_parser.hpp

Problem: Conflicting Names

• Multiple free functions with the same name and parameter list
• Causes a name conflict
• Program cannot be built Converter
• Means that pdf_parser.hpp and yaml_parser.hpp cannot be used in the same code
• We should not restrict the potential environment for our code to be used in

Problem: Conflicting Names, Solution?

• Has a prefix, pdf_ for the pdf parser, yaml_ for the yaml parser
• Prefix would be used for all functions provided
• Solves the conflict
• More of a C-library form
• Could also extend to class names, variables, and other program elements that we name
• However, we have better options available
• We should not restrict the potential environment for our code to be used in

Better Solution: Namespaces

• A language feature to group functions and provide an organizing name
• Can contain:
• free functions
• variables
• classes
• typedef

Cumulative Namespaces

• All of the contents of a particular namespace do not have to be declared at the same time
• They can even be declared in separate files

Namespace Aliases

• The type optional exists in both std:: and boost::
• The namespace opt can refer to either boost or std
• Does abstract the choice but requires tracing back when needed
• Useful in conversion or potential flexibility
• Not a long-term solution due to the abstraction cost

Another Option: Static Methods of a Class

• static class methods do not have access to data members/fields
• They do have access to static data members/fields
• We will consider that another time
• For now, considering methods that could be free functions but, due to naming issues, are not
• No advantage over namespaces, except that it may be joined with non-static member functions
• We can easily put classes in a namespace
• We can also nest classes ("inner classes"). However, in C++, this often causes more pain than it's worth. Every time I've done this, I ripped them out at some point.