switch.lua

-- This function attempts to emulate switch statements used in programming languages such as C++.
-- First argument is the case in the statement to run. This is a value to index an element in a table. Indexes can be any number or string.
-- Second argument is a table containing functions representing each case. This only executes the case indexed by the first argument. Setting a case equal to a number or string represents a pointer to a different case function. This is to avoid copy and pasting functions. Pointers cannot point to pointers. Unlike C++ switch statements, these switch statements can be nested within switch statements.
-- Third argument is the default case. This is run if none of the other cases are executed.
-- Additional arguments are passed to the case functions.

switch = function(case, cases, defCase, ...)
    if cases[case] then
        if type(cases[case]) == "function" then return cases[case](...)
        elseif type(cases[case]) == "number" or type(cases[case]) == "string" then return cases[cases[case] ](...)
        else error("Case element must be a number, string, or function.", 2) end
    else
        if defCase then return defCase(...)
        else error("Undefined case '"..tostring(case).."'.", 2) end
    end
end

-- Examples of the switch statement in use.
local function testProgram()
    for a = 0, 5 do
        switch(a, {
            [0] = function()
                print('h')
            end,
            [1] = function()
                print('e')
            end,
            [2] = function()
                print('l')
            end,
            [3] = 2, -- This case points to case [2], so case [3] will run the function for case [2]. Another case may not point to case [3], or else the program will throw an error.
            [4] = function()
                print('o')
            end
        }, function(punctuation)
            print(punctuation)
        end, '.')
    end

    switch("pear", {
        ["apple"] = function()
            print("Hello world")
        end,
        pear = function()
            print("Switch statements are neat.")
        end
    }, function() end)

    switch("apple", {
        ["fruit"] = function()
            print("Hello world")
        end,
        veggie = function()
            print("Switch statements are neat.")
        end,
        apple = "fruit"
    }, function() end)
end

-- Uncomment the line below to run the test program function.
-- testProgram()

-- This program was written for ComputerCraft, but I have not used any functions that are not standard to Lua, so it should work with any Lua application.
-- This program was tested in CCEmuX which is a ComputerCraft "emulator" so that I don't have to start up all of Minecraft every time I want to make something in CC that's not explicitly Minecraft related.
-- You can use this with ComputerCraft's os.loadAPI() to load the Class() function into a separate program file.
-- Alternatively, you can use the require() function, which does effectively the same thing but is newer to ComputerCraft.
-- If you can I highly recommend using require() instead because it's way more efficient, and it's a standard Lua function so it should work beyond ComputerCraft, but I have not tested this to be sure.

--[[ Changelog
    2022/06/22: This switch statement will be deprecated for performance reasons. I realized that this is actually 2 times slower than regular if statements.
    2022/03/03:
        If a default case is not defined and the given case is also not defined, an error will be thrown for the invalid case.
    2021/07/28:
        Initial release.
]]