Tom Hines (writinThatCode.com)

A number of years ago, I was helping someone on DaniWeb with some code that was (probably) more than they expected.
I never got closure on the code because it seemed the requester didn’t understand to use Visual Studio.
ANYWAY:
I recently revisited that code and realized how differently I would have done things if I created it today.
It’s like that old cartoon from NotInventedHere.com on 4/20/2010 where one character can’t stand to see his old code:

Well, I had the same reaction to mine (as I frequently do) and so I rewrote portions of it.
Luckily, it was short and I knew SPECIFICALLY what I wanted done (for now).

I figured I’d go ahead and post it for future reference (when I once again can’t stand it).

This code puts into practice multiple techniques for using Linq and IEnumerable in C++/CLI.
The program itself is a simple shell-program where the user has a command-line and can enter
some simple commands.

This was probably someone’s homework, but the implementation I demonstrated might not have been
something he/she could have turned in.  LOL.

// DW_393014.cpp : main project file.
#include "stdafx.h"
using namespace System;
using namespace System::Collections::Generic;
using namespace System::IO;
using namespace System::Linq;
 
public ref class CCommands
{
private:
	//
	static void _doShowDir(void)
	{
		Console::WriteLine(
			String::Join("\r\n",
				Enumerable::ToArray<String^>(
					Directory::GetFiles(
						Directory::GetCurrentDirectory()))));
	}
	//
	static void _doHelp()
	{
		Console::WriteLine("Commands are: " +
			String::Join(", ",
				Enumerable::ToArray<String^>(
					Enumerable::Select(arr_kvp_s2aCommands, getKeyFromKvpS2a))) + ", quit, exit");
	}
	//
	static Action^ _getActFromKvpS2aJoin(KeyValuePair<String^, Action^> kvpS2a, String^) { return kvpS2a.Value; }
	//
	static Action^ _clear = gcnew Action(Console::Clear);
	static Action^ _help = gcnew Action(_doHelp);
	static Action^ _showDir = gcnew Action(_doShowDir);
	//
	static String^ _getKeyFromKvpS2a(KeyValuePair<String^, Action^> kvp_s2a) { return kvp_s2a.Key; }
	static String^ _getStringAsString(String^ str) { return str; }
	//
	static bool _notNothing(Action^ act) { return nullptr != act; }
	static void _doNothing(){}
public:
	static Func<KeyValuePair<String^, Action^>, String^>^ getKeyFromKvpS2a =
		gcnew Func<KeyValuePair<String^, Action^>, String^>(_getKeyFromKvpS2a);
 
	static Func<String^, String^>^ getStringAsString = gcnew Func<String^, String^>(_getStringAsString);
 
	static Func<KeyValuePair<String^, Action^>, String^, Action^>^ getActFromKvpS2aJoin =
		gcnew Func<KeyValuePair<String^, Action^>, String^, Action^>(_getActFromKvpS2aJoin);
 
	static String^ NowTime(DateTime^ dt)
	{
		return String::Format("{0}:{1}:{2}",
			dt->Hour.ToString("D2"),
			dt->Minute.ToString("D2"),
			dt->Second.ToString("D2"));
	}
 
	//
	static IEnumerable<KeyValuePair<String^, Action^>>^ arr_kvp_s2aCommands =
		gcnew array<KeyValuePair<String^, Action^>>
		{
			KeyValuePair<String^, Action^>("spy", _showDir),
			KeyValuePair<String^, Action^>("wipe", _clear),
			KeyValuePair<String^, Action^>("help", _help),
		};
 
	static Action^ DoNothing = gcnew Action(_doNothing);
	static Func<Action^, bool>^ IsSomething = gcnew Func<Action^, bool>(_notNothing);
};
 
int main(void)
{	//array<System::String ^> ^args)
	Console::WriteLine(L"Welcome to CLI Shell (v1.0)\n");
 
	array<String^>^ arr_strQuitExit = { "exit", "quit" };
	String^ strCommand = "";
 
	while (!Enumerable::Contains<String^>(arr_strQuitExit, strCommand))
	{
		Console::Write("{0}>: ", CCommands::NowTime(DateTime::Now));
		strCommand = Console::ReadLine()->ToLower();
 
		//////////////////////////////////////////////////////////////////////////////
		// Invoke the first non-null Action that matches the command
		// If no match, call the DoNothing action.
		Enumerable::First<Action^>
		(	// construct pieces ensures no nulls
			gcnew array <Action^>
			{	// [0]=desired command, [1]=fall-back
				Enumerable::FirstOrDefault<Action^>
				( // returns nullptr if no matching command
					Enumerable::Join<KeyValuePair<String^, Action^>, String^, String^, Action^>
					(
						CCommands::arr_kvp_s2aCommands,
						gcnew array <String^> { strCommand }, // array of 1
						CCommands::getKeyFromKvpS2a,		// get the Key (string)
						CCommands::getStringAsString,    // return the string
						CCommands::getActFromKvpS2aJoin  // (KVP, STR) => KVP->Key
					)
				),
				CCommands::DoNothing // when no match or nullptr
			},
			CCommands::IsSomething // not nullptr
		)->Invoke();
	}
	//
	return 0;
}