class, module, coroutine, begining error

+ some correction and addition.
2023-01-16 00:47:06 +01:00 · 2023-01-16 00:47:06 +01:00 · 74b02df3c1
commit 74b02df3c1
parent 655ce78eee
3 changed files with 317 additions and 14 deletions
--- a/README.md
+++ b/README.md
@ -1,6 +1,7 @@
 # cheat-sheet-lua

-Here is the IO-Project cheat sheet to quickly learn the "Lua" programming language
+Here is the IO-Project cheat sheet to quickly learn the "Lua" programming language.
+I suggest you to consult the documentation of lua for more information on the language, it is available by following [this link](https://www.lua.org/manual/5.3/).

 ## Table of contents

@ -8,7 +9,7 @@ Use this table of contents to travel more easily through this cheat sheet.

 - [cheat-sheet-lua](#cheat-sheet-lua)
  - [Table of contents](#table-of-contents)
-  - [The basics](#the-basics)
+  - [Basics](#basics)
    - [Code comments](#code-comments)
    - [Variables and loop](#variables-and-loop)
    - [Functions](#functions)
@ -16,8 +17,13 @@ Use this table of contents to travel more easily through this cheat sheet.
    - [Tables, Array, dict..](#tables-array-dict)
      - [Metatables and metamethods](#metatables-and-metamethods)
      - [Class-like tables and inheritance.](#class-like-tables-and-inheritance)
+    - [Coroutine](#coroutine)
+    - [Error handling](#error-handling)
+    - [Modules](#modules)

-## The basics
+## Basics
+
+> We'll now introduce the basics of lua, starting with comments, variables, loops and functions.

 ### Code comments

@ -163,14 +169,13 @@ print 'hello'  -- Works fine.

 ## Advanced

+> Let's move on to more advanced notions. With the notion of table, class, module, coroutine, meta-programming and module.
+
 ### Tables, Array, dict..

-````lua
-- Tables = Lua's only compound data structure;
--          they are associative arrays.
-- Similar to php arrays or js objects, they are
-- hash-lookup dicts that can also be used as lists.
+Tables are the only compound data structure in Lua, they are associative arrays. Similar to php arrays or js objects, they are hash-lookup dicts that can also be used as lists.

+````lua
 -- Using tables as dictionaries / maps:

 -- Dict literals have string keys by default:
@ -218,11 +223,9 @@ end

 #### Metatables and metamethods

-````lua
-- A table can have a metatable that gives the table
-- operator-overloadish behavior. Later we'll see
-- how metatables support js-prototypey behavior.
+A table can have a metatable that gives the table operator-overloadish behavior. Later we'll see how metatables support js-prototypey behavior.

+````lua
 f1 = {a = 1, b = 2}  -- Represents the fraction a/b.
 f2 = {a = 2, b = 3}

@ -282,4 +285,194 @@ eatenBy = myFavs.animal  -- works! thanks, metatable
 -- __call(a, ...)                  for a(...)
 ````

-#### Class-like tables and inheritance.
+#### Class-like tables and inheritance.
+
+Classes aren't built in, there are different ways to emulate them with tables and metatables.
+The different ways to define a class in Lua are not easy to understand, so I suggest you to look at the [following document](support/class.lua) implementing 3 types of class definition. The last one being the one I chose (my preferred method).
+
+````lua
+-- Explanation for this example is below it.
+Dog = {}                                   -- 1.
+
+function Dog:new()                         -- 2.
+  newObj = {sound = 'woof'}                -- 3.
+  self.__index = self                      -- 4.
+  return setmetatable(newObj, self)        -- 5.
+end
+
+function Dog:makeSound()                   -- 6.
+  print('I say ' .. self.sound)
+end
+
+mrDog = Dog:new()                          -- 7.
+mrDog:makeSound()  -- 'I say woof'         -- 8.
+
+-- 1. Dog acts like a class; it's really a table.
+-- 2. function tablename:fn(...) is the same as
+--    function tablename.fn(self, ...)
+--    The : just adds a first arg called self.
+--    Read 7 & 8 below for how self gets its value.
+-- 3. newObj will be an instance of class Dog.
+-- 4. self = the class being instantiated. Often
+--    self = Dog, but inheritance can change it.
+--    newObj gets self's functions when we set both
+--    newObj's metatable and self's __index to self.
+-- 5. Reminder: setmetatable returns its first arg.
+-- 6. The : works as in 2, but this time we expect
+--    self to be an instance instead of a class.
+-- 7. Same as Dog.new(Dog), so self = Dog in new().
+-- 8. Same as mrDog.makeSound(mrDog); self = mrDog.
+
+----------------------------------------------------
+
+-- Inheritance example:
+LoudDog = Dog:new()                         -- 1.
+
+function LoudDog:makeSound()
+  s = self.sound .. ' '                     -- 2.
+  print(s .. s .. s)
+end
+
+seymour = LoudDog:new()                     -- 3.
+seymour:makeSound()  -- 'woof woof woof'    -- 4.
+
+-- 1. LoudDog gets Dog's methods and variables.
+-- 2. self has a 'sound' key from new(), see 3.
+-- 3. Same as LoudDog.new(LoudDog), and converted to
+--    Dog.new(LoudDog) as LoudDog has no 'new' key,
+--    but does have __index = Dog on its metatable.
+--    Result: seymour's metatable is LoudDog, and
+--    LoudDog.__index = LoudDog. So seymour.key will
+--    = seymour.key, LoudDog.key, Dog.key, whichever
+--    table is the first with the given key.
+-- 4. The 'makeSound' key is found in LoudDog; this
+--    is the same as LoudDog.makeSound(seymour).
+
+-- If needed, a subclass's new() is like the base's:
+function LoudDog:new()
+  newObj = {}
+  -- set up newObj
+  self.__index = self
+  return setmetatable(newObj, self)
+end
+````
+
+### Coroutine
+
+Let's turn now to coroutines. Coroutines are functions that can be suspended and resumed at a later time. They are used to implement iterators, generators and event loops and represent a line of execution with its own stack. In other words, they can be compared to threads.
+
+````lua
+-- Create a coroutine that prints 'Hello' and then stops.
+coHi = coroutine.create(function () print('Hello') end)
+print(coHi)  -- thread: 0x7f9c0c00a0c0
+
+-- Coroutine status can be 'suspended', 'running' or 'dead'.
+-- The coroutine is created in the 'suspended' state.
+
+-- Resume the coroutine. It will print 'Hello' and stop.
+coroutine.resume(coHi)  -- return 'true'
+print(coroutine.status(coHi))  -- 'dead'
+
+-- We can also pass arguments to the coroutine.
+-- The arguments of the first resume are passed to the
+-- function of the coroutine. The following arguments
+-- are passed to the yield function.
+routine = coroutine.create(function (a, b, c)
+  print('first print: ', a, b, c)
+  print('yield1: ', coroutine.yield())
+  print('yield2: ', coroutine.yield('a variable'))
+  return(a+b+c)
+end)
+
+-- will run the coroutine until the first yield.
+coroutine.resume(routine, 1, 2, 3)
+-- run the coroutine until the second yield passing
+-- the arguments 4, 5 and 6 to the 1er yield and
+-- retrieve the return value of the second yield.
+print('out routine: ' , coroutine.resume(routine, 4, 5, 6))
+-- this will run out the second yield and made the
+-- adition of 'a+b+c'  and kill the coroutine.
+print(coroutine.resume(routine, 7, 8, 9)) -- 1+2+3 = '6'
+
+-- All these steps will print:
+--[[
+    first print:    1       2       3
+    yield1:         4       5       6
+    out routine:    true    a variable
+    yield2:         7       8       9
+    true    6
+--]]
+````
+
+### Error handling
+
+Lua allows low-level error handling with the `error` function and high-level error handling with the `assert` function. The `error` function raises an error and handles it with the `pcall` or `xpcall` function. The `assert` function checks a condition and raises an error if the condition is not met.
+
+````lua
+
+
+
+-- Throw an error if the first argument is false
+-- the second argument is the error message.
+assert(type(firstvariable) = 'string', 'not a string')
+
+-- TODO to continue
+
+````
+
+### Modules
+
+Modules are a way to organize your code. They are a way to group functions and variables together in a single file. You can then use the module in other files by using the `require` function.
+
+````lua
+-- Suppose the file mod.lua looks like this:
+local M = {}
+
+local function sayMyName()
+  print('Hrunkner')
+end
+
+function M.sayHello()
+  print('Why hello there')
+  sayMyName()
+end
+
+return M  -- Return the table M.
+
+-- Another file can use mod.lua's functionality:
+local mod = require('mod')  -- Run the file mod.lua.
+
+-- require is the standard way to include modules.
+-- require acts like:     (if not cached; see below)
+local mod = (function ()
+  <contents of mod.lua>
+end)()
+-- It's like mod.lua is a function body, so that
+-- locals inside mod.lua are invisible outside it.
+
+-- This works because mod here = M in mod.lua:
+mod.sayHello()  -- Says hello to Hrunkner.
+
+-- This is wrong, sayMyName only exists in mod.lua:
+mod.sayMyName()  -- error
+
+-- require's return values are cached so a file is
+-- run at most once, even when require'd many times.
+
+-- Suppose mod2.lua contains "print('Hi!')".
+local a = require('mod2')  -- Prints Hi!
+local b = require('mod2')  -- Doesn't print; a=b.
+
+-- dofile is like require without caching:
+dofile('mod2.lua')  --> Hi!
+dofile('mod2.lua')  --> Hi! (runs it again)
+
+-- loadfile loads a lua file but doesn't run it yet.
+f = loadfile('mod2.lua')  -- Call f() to run it.
+
+-- loadstring is loadfile for strings.
+g = loadstring('print(343)')  -- Returns a function.
+g()  -- Prints out '343', nothing printed before now.
+
+````
+
--- a/support/class.lua
+++ b/support/class.lua
@ -0,0 +1,102 @@
+
+-- ============================================================================
+-- This is a simple Person class (Raw example without synthetic sugar).
+-- ============================================================================
+Person1 = {}
+
+-- Constructor
+function Person1.new(self, name, age)
+  local o = {}
+  self.__index = self
+  setmetatable(o, self)
+  o.name = name
+  o.age = age
+  return o
+end
+
+-- Methods
+function Person1.getName(self)
+  return self.name
+end
+
+function Person1.getAge(self)
+  return self.age
+end
+
+-- Usage
+local instance = Person1.new(Person1, "John", 30)
+print('name: ' .. instance.getName(instance))  -- John
+print('age: ' .. instance.getAge(instance))  -- 30
+
+-- Garbage collection
+Person1 = nil
+instance = nil
+
+
+-- ============================================================================
+-- This is a simple Person class (Synthetic sugar example).
+-- ============================================================================
+Person2 = {}
+
+-- Constructor
+function Person2:new(name, age)
+  local o = {}
+  self.__index = self
+  setmetatable(o, self)
+  o.name = name
+  o.age = age
+  return o
+end
+
+-- Methods
+function Person2:getName()
+  return self.name
+end
+
+function Person2:getAge()
+  return self.age
+end
+
+-- Usage
+local instance = Person2:new("John Doe", 50)
+print('name: ' .. instance:getName())  -- John Doe
+print('age: ' .. instance:getAge())  -- 50
+
+-- Garbage collection
+Person2 = nil
+instance = nil
+
+
+-- ============================================================================
+-- This is my class definition method (with Synthetic sugar example).
+-- ============================================================================
+Person = {}
+
+-- Constructor
+function Person:new(name, age)
+  local this = setmetatable({}, {__index = self})
+  this.name = name or 'EndMove'
+  this.age = age or 20
+  return this
+end
+
+-- Methods
+function Person:getFName()
+  return 'name: ' .. self.name
+end
+
+function Person:getFAge()
+  return 'age: ' .. self.age
+end
+
+-- Usage
+local instance = Person:new("Gashy", 21)
+print(instance:getFName())  -- name: Gashy
+print(instance:getFAge())  -- age: 21
+
+-- Garbage collection
+Person = nil
+instance = nil
+
+-- ============================================================================
+-- Thanks for reading!
--- a/support/while.lua
+++ b/support/while.lua
@ -1,3 +1,8 @@
+
+-- ============================================================================
+-- Let's study the different loops offered by the Lua language.
+-- ============================================================================
+
 -- Jeb while loop
 local jebSum = 0
 print('jeb : '..jebSum)
@ -38,4 +43,7 @@ while true do
  print('Breaking out in')
  if true then break end
 end
-print('Breaking out -> Done')
+print('Breaking out -> Done')
+
+-- ============================================================================
+-- Thanks for reading!