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C++17 in Detail: A Deep Dive

The Use Case

Explore how to refactor code by replacing output parameters with tuples, structs, std optional, and std variant in C++17. Understand how these features improve function design, reduce duplication, and enhance error handling to write clearer and more maintainable code.

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​Consider a function that takes the current mouse selection for a game. The function scans the selected range and computes several outputs:

  • the number of animating objects
  • if there are any civil units in the selection
  • if there are any combat units in the selection

The existing code looks like this:

C++
class ObjSelection
{
public:
  bool IsValid() const { return true; }
  // more code...
};
bool CheckSelectionVer1(const ObjSelection &objList, bool *pOutAnyCivilUnits, bool *pOutAnyCombatUnits, int *pOutNumAnimating)
{
    if (!objList.IsValid())
        return false;
    
    // local variables:
    int numCivilUnits = 0;
    int numCombat = 0;
    int numAnimating = 0;
    
    // scan...
    
    // set values:
    if (pOutAnyCivilUnits)
        *pOutAnyCivilUnits = numCivilUnits > 0;
        
    if (pOutAnyCombatUnits)
        *pOutAnyCombatUnits = numCombat > 0;
    
    if (pOutNumAnimating)
        *pOutNumAnimating = numAnimating;
    
    return true;
}

As you can see above, the function uses a lot of output parameters (in the ...