Why does the code use if-else instead of switch-case?

[donno2048]

I guess

terminal/src/host/CommandNumberPopup.cpp

Lines 135 to 148 in 11b810e

	else if (wch == UNICODE_BACKSPACE)
	{
	_handleBackspace(cookedReadData);
	}
	else if (wch == VK_ESCAPE)
	{
	_handleEscape(cookedReadData);
	break;
	}
	else if (wch == UNICODE_CARRIAGERETURN)
	{
	_handleReturn(cookedReadData);
	break;
	}

terminal/src/host/ConsoleArguments.cpp

Lines 435 to 470 in 11b810e

	else if (arg == SIGNAL_HANDLE_ARG)
	{
	std::wstring signalHandleVal;
	hr = s_GetArgumentValue(args, i, &signalHandleVal);
	if (SUCCEEDED(hr))
	{
	hr = s_ParseHandleArg(signalHandleVal, _signalHandle);
	}
	}
	else if (arg == FORCE_V1_ARG)
	{
	// -ForceV1 command line switch for NTVDM support
	_forceV1 = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}
	else if (arg == FORCE_NO_HANDOFF_ARG)
	{
	// Prevent default application handoff to a different console/terminal
	_forceNoHandoff = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}
	else if (arg == COM_SERVER_ARG)
	{
	_runAsComServer = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}
	else if (arg == PASSTHROUGH_ARG)
	{
	_passthroughMode = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}

terminal/src/host/ConsoleArguments.cpp

Lines 478 to 533 in 11b810e

	else if (arg == VT_MODE_ARG)
	{
	hr = s_GetArgumentValue(args, i, &_vtMode);
	}
	else if (arg == WIDTH_ARG)
	{
	hr = s_GetArgumentValue(args, i, &_width);
	}
	else if (arg == HEIGHT_ARG)
	{
	hr = s_GetArgumentValue(args, i, &_height);
	}
	else if (arg == FEATURE_ARG)
	{
	hr = s_HandleFeatureValue(args, i);
	}
	else if (arg == HEADLESS_ARG)
	{
	_headless = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}
	else if (arg == INHERIT_CURSOR_ARG)
	{
	_inheritCursor = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}
	else if (arg == RESIZE_QUIRK)
	{
	_resizeQuirk = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}
	else if (arg == WIN32_INPUT_MODE)
	{
	_win32InputMode = true;
	s_ConsumeArg(args, i);
	hr = S_OK;
	}
	else if (arg == CLIENT_COMMANDLINE_ARG)
	{
	// Everything after this is the explicit commandline
	hr = _GetClientCommandline(args, i, true);
	break;
	}
	// TODO: handle the rest of the possible params (MSFT:13271366, MSFT:13631640)
	// TODO: handle invalid args
	// e.g. "conhost --foo bar" should not make the clientCommandline "--foo bar"
	else
	{
	// If we encounter something that doesn't match one of our other
	// args, then it's the start of the commandline
	hr = _GetClientCommandline(args, i, false);
	break;
	}

terminal/src/inc/til/string.h

Lines 16 to 23 in 11b810e

	else if (ch == 0x20)
	{
	ch = 0x2423; // replace space with ␣
	}
	else if (ch == 0x7f)
	{
	ch = 0x2421; // replace del with ␡
	}

make some sense but

terminal/src/tools/echokey/main.cpp

Lines 56 to 173 in 11b810e

	void toPrintableBufferA(char c, char* printBuffer, int* printCch)
	{
	if (c == '\x1b')
	{
	printBuffer[0] = '^';
	printBuffer[1] = '[';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	else if (c == '\x03')
	{
	printBuffer[0] = '^';
	printBuffer[1] = 'C';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	else if (c == '\x0')
	{
	printBuffer[0] = '\\';
	printBuffer[1] = '0';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	else if (c == '\r')
	{
	printBuffer[0] = '\\';
	printBuffer[1] = 'r';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	else if (c == '\n')
	{
	printBuffer[0] = '\\';
	printBuffer[1] = 'n';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	else if (c == '\t')
	{
	printBuffer[0] = '\\';
	printBuffer[1] = 't';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	else if (c == '\b')
	{
	printBuffer[0] = '\\';
	printBuffer[1] = 'b';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	else
	{
	printBuffer[0] = (char)c;
	printBuffer[1] = ' ';
	printBuffer[2] = '\0';
	*printCch = 2;
	}
	}
	void toPrintableBufferW(wchar_t c, wchar_t* printBuffer, int* printCch)
	{
	if (c == L'\x1b')
	{
	printBuffer[0] = L'^';
	printBuffer[1] = L'[';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	else if (c == '\x03')
	{
	printBuffer[0] = L'^';
	printBuffer[1] = L'C';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	else if (c == '\x0')
	{
	printBuffer[0] = L'\\';
	printBuffer[1] = L'0';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	else if (c == '\r')
	{
	printBuffer[0] = L'\\';
	printBuffer[1] = L'r';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	else if (c == '\n')
	{
	printBuffer[0] = L'\\';
	printBuffer[1] = L'n';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	else if (c == '\t')
	{
	printBuffer[0] = L'\\';
	printBuffer[1] = L't';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	else if (c == '\b')
	{
	printBuffer[0] = L'\\';
	printBuffer[1] = L'b';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	else
	{
	printBuffer[0] = (wchar_t)c;
	printBuffer[1] = L' ';
	printBuffer[2] = L'\0';
	*printCch = 2;
	}
	}

terminal/src/propsheet/ColorControl.cpp

Lines 7 to 26 in 11b810e

	COLORREF GetColorForItem(const int itemId)
	{
	if (itemId >= IDD_COLOR_1 && itemId <= IDD_COLOR_16)
	{
	return AttrToRGB(itemId - IDD_COLOR_1);
	}
	else if (itemId == IDD_TERMINAL_FGCOLOR)
	{
	return g_fakeForegroundColor;
	}
	else if (itemId == IDD_TERMINAL_BGCOLOR)
	{
	return g_fakeBackgroundColor;
	}
	else if (itemId == IDD_TERMINAL_CURSOR_COLOR)
	{
	return g_fakeCursorColor;
	}
	return RGB(0xff, 0x0, 0xff);
	}

?

[zadjii-msft]

I don't think there's necessarily a reason. I suppose I write a lot of python in my free time, so I write the if/else's instinctively, but those samples I think predate my tenure on the project 😅 Any reason you're asking?

[donno2048]

It's just that a switch case is more efficient so why not use it?

[DHowett]

A few reasons:

1. Most compilers these days are capable of optimizing long if chains to the same machine code as a switch-case, which makes the conversion unnecessary
2. We do not have unlimited time to go refactor every bit of old code, and it works as-is
3. Even if automatic optimization were not possible, the snippets you've identified are not in hot paths and do not need to be more efficient than they are.

Some of the examples you listed include range checks (the ones in til/string and the one in ColorControl, primarily) which would only suffer from conversion to switch-case. As an example:

COLORREF GetColorForItem(const int itemId) 
{
    switch (itemId)
    {
    case IDD_TERMINAL_FGCOLOR:
        return g_fakeForegroundColor; 
    case IDD_TERMINAL_BGCOLOR:
        return g_fakeBackgroundColor; 
    case IDD_TERMINAL_CURSOR_COLOR:
        return g_fakeCursorColor; 
    default:
        if (itemId >= IDD_COLOR_1 && itemId <= IDD_COLOR_16) 
        { 
            return AttrToRGB(itemId - IDD_COLOR_1); 
        } 
        break;
    }
    return RGB(0xff, 0x0, 0xff); 
}

Given the range, default cannot be comprehensive or exhaustive... so we've traded some clarity away to gain the illusion of convenience.

[MHKarami97]

To sum it up, if number of conditions is more than 5 or so, prefer SWITCH over IF, otherwise use whatever looks better.

more info : https://stackoverflow.com/a/395965/10233323