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Merge pull request #3410 from MegaBedder/patch-1
[lua/en] Update from gist/tylerneylon
This commit is contained in:
Divay Prakash
GitHub
commit
09b68aa58a
@ -12,13 +12,15 @@ filename: learnlua.lua
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Adding two ['s and ]'s makes it a
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multi-line comment.
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--]]
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- 1. Variables and flow control.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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num = 42 -- All numbers are doubles.
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-- Don't freak out, 64-bit doubles have 52 bits for storing exact int
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-- values; machine precision is not a problem for ints that need < 52 bits.
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-- Don't freak out, 64-bit doubles have 52 bits for
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-- storing exact int values; machine precision is
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-- not a problem for ints that need < 52 bits.
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s = 'walternate' -- Immutable strings like Python.
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t = "double-quotes are also fine"
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@ -58,15 +60,10 @@ aBoolValue = false
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-- Only nil and false are falsy; 0 and '' are true!
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if not aBoolValue then print('twas false') end
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-- 'or' and 'and' are short-circuited. This is similar to the a?b:c operator
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-- in C/js:
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-- 'or' and 'and' are short-circuited.
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-- This is similar to the a?b:c operator in C/js:
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ans = aBoolValue and 'yes' or 'no' --> 'no'
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-- BEWARE: this only acts as a ternary if the value returned when the condition
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-- evaluates to true is not `false` or Nil
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iAmNotFalse = (not aBoolValue) and false or true --> true
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iAmAlsoNotFalse = (not aBoolValue) and true or false --> true
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karlSum = 0
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for i = 1, 100 do -- The range includes both ends.
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karlSum = karlSum + i
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@ -84,19 +81,20 @@ repeat
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num = num - 1
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until num == 0
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- 2. Functions.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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function fib(n)
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if n < 2 then return n end
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if n < 2 then return 1 end
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return fib(n - 2) + fib(n - 1)
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end
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-- Closures and anonymous functions are ok:
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function adder(x)
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-- The returned function is created when adder is called, and remembers the
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-- value of x:
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-- The returned function is created when adder is
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-- called, and remembers the value of x:
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return function (y) return x + y end
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end
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a1 = adder(9)
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@ -104,9 +102,10 @@ a2 = adder(36)
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print(a1(16)) --> 25
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print(a2(64)) --> 100
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-- Returns, func calls, and assignments all work with lists that may be
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-- mismatched in length. Unmatched receivers are nil; unmatched senders are
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-- discarded.
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-- Returns, func calls, and assignments all work
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-- with lists that may be mismatched in length.
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-- Unmatched receivers are nil;
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-- unmatched senders are discarded.
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x, y, z = 1, 2, 3, 4
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-- Now x = 1, y = 2, z = 3, and 4 is thrown away.
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@ -119,15 +118,13 @@ end
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x, y = bar('zaphod') --> prints "zaphod nil nil"
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-- Now x = 4, y = 8, values 15..42 are discarded.
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-- Functions are first-class, may be local/global. These are the same:
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-- Functions are first-class, may be local/global.
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-- These are the same:
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function f(x) return x * x end
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f = function (x) return x * x end
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-- And so are these:
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local function g(x) return math.sin(x) end
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local g = function(x) return math.sin(x) end
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-- Equivalent to local function g(x)..., except referring to g in the function
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-- body won't work as expected.
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local g; g = function (x) return math.sin(x) end
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-- the 'local g' decl makes g-self-references ok.
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@ -136,16 +133,15 @@ local g; g = function (x) return math.sin(x) end
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-- Calls with one string param don't need parens:
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print 'hello' -- Works fine.
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-- Calls with one table param don't need parens either (more on tables below):
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print {} -- Works fine too.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- 3. Tables.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- Tables = Lua's only compound data structure; they are associative arrays.
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-- Similar to php arrays or js objects, they are hash-lookup dicts that can
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-- also be used as lists.
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-- Tables = Lua's only compound data structure;
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-- they are associative arrays.
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-- Similar to php arrays or js objects, they are
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-- hash-lookup dicts that can also be used as lists.
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-- Using tables as dictionaries / maps:
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@ -161,13 +157,14 @@ t.key2 = nil -- Removes key2 from the table.
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u = {['@!#'] = 'qbert', [{}] = 1729, [6.28] = 'tau'}
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print(u[6.28]) -- prints "tau"
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-- Key matching is basically by value for numbers and strings, but by identity
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-- for tables.
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-- Key matching is basically by value for numbers
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-- and strings, but by identity for tables.
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a = u['@!#'] -- Now a = 'qbert'.
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b = u[{}] -- We might expect 1729, but it's nil:
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-- b = nil since the lookup fails. It fails because the key we used is not the
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-- same object as the one used to store the original value. So strings &
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-- numbers are more portable keys.
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-- b = nil since the lookup fails. It fails
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-- because the key we used is not the same object
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-- as the one used to store the original value. So
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-- strings & numbers are more portable keys.
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-- A one-table-param function call needs no parens:
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function h(x) print(x.key1) end
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@ -187,15 +184,16 @@ v = {'value1', 'value2', 1.21, 'gigawatts'}
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for i = 1, #v do -- #v is the size of v for lists.
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print(v[i]) -- Indices start at 1 !! SO CRAZY!
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end
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-- A 'list' is not a real type. v is just a table with consecutive integer
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-- keys, treated as a list.
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-- A 'list' is not a real type. v is just a table
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-- with consecutive integer keys, treated as a list.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- 3.1 Metatables and metamethods.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- A table can have a metatable that gives the table operator-overloadish
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-- behaviour. Later we'll see how metatables support js-prototype behaviour.
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-- A table can have a metatable that gives the table
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-- operator-overloadish behavior. Later we'll see
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-- how metatables support js-prototypey behavior.
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f1 = {a = 1, b = 2} -- Represents the fraction a/b.
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f2 = {a = 2, b = 3}
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@ -205,7 +203,7 @@ f2 = {a = 2, b = 3}
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metafraction = {}
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function metafraction.__add(f1, f2)
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local sum = {}
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sum = {}
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sum.b = f1.b * f2.b
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sum.a = f1.a * f2.b + f2.a * f1.b
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return sum
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@ -216,9 +214,10 @@ setmetatable(f2, metafraction)
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s = f1 + f2 -- call __add(f1, f2) on f1's metatable
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-- f1, f2 have no key for their metatable, unlike prototypes in js, so you must
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-- retrieve it as in getmetatable(f1). The metatable is a normal table with
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-- keys that Lua knows about, like __add.
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-- f1, f2 have no key for their metatable, unlike
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-- prototypes in js, so you must retrieve it as in
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-- getmetatable(f1). The metatable is a normal table
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-- with keys that Lua knows about, like __add.
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-- But the next line fails since s has no metatable:
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-- t = s + s
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@ -230,12 +229,11 @@ myFavs = {food = 'pizza'}
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setmetatable(myFavs, {__index = defaultFavs})
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eatenBy = myFavs.animal -- works! thanks, metatable
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--------------------------------------------------------------------------------
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-- Direct table lookups that fail will retry using the metatable's __index
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-- value, and this recurses.
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-- Direct table lookups that fail will retry using
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-- the metatable's __index value, and this recurses.
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-- An __index value can also be a function(tbl, key) for more customized
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-- lookups.
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-- An __index value can also be a function(tbl, key)
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-- for more customized lookups.
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-- Values of __index,add, .. are called metamethods.
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-- Full list. Here a is a table with the metamethod.
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@ -256,19 +254,19 @@ eatenBy = myFavs.animal -- works! thanks, metatable
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-- __newindex(a, b, c) for a.b = c
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-- __call(a, ...) for a(...)
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- 3.2 Class-like tables and inheritance.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- Classes aren't built in; there are different ways to make them using
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-- tables and metatables.
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-- Classes aren't built in; there are different ways
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-- to make them using tables and metatables.
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-- Explanation for this example is below it.
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Dog = {} -- 1.
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function Dog:new() -- 2.
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local newObj = {sound = 'woof'} -- 3.
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newObj = {sound = 'woof'} -- 3.
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self.__index = self -- 4.
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return setmetatable(newObj, self) -- 5.
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end
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@ -281,59 +279,62 @@ mrDog = Dog:new() -- 7.
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mrDog:makeSound() -- 'I say woof' -- 8.
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-- 1. Dog acts like a class; it's really a table.
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-- 2. "function tablename:fn(...)" is the same as
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-- "function tablename.fn(self, ...)", The : just adds a first arg called
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-- self. Read 7 & 8 below for how self gets its value.
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-- 2. function tablename:fn(...) is the same as
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-- function tablename.fn(self, ...)
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-- The : just adds a first arg called self.
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-- Read 7 & 8 below for how self gets its value.
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-- 3. newObj will be an instance of class Dog.
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-- 4. "self" is the class being instantiated. Often self = Dog, but inheritance
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-- can change it. newObj gets self's functions when we set both newObj's
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-- metatable and self's __index to self.
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-- 4. self = the class being instantiated. Often
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-- self = Dog, but inheritance can change it.
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-- newObj gets self's functions when we set both
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-- newObj's metatable and self's __index to self.
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-- 5. Reminder: setmetatable returns its first arg.
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-- 6. The : works as in 2, but this time we expect self to be an instance
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-- instead of a class.
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-- 6. The : works as in 2, but this time we expect
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-- self to be an instance instead of a class.
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-- 7. Same as Dog.new(Dog), so self = Dog in new().
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-- 8. Same as mrDog.makeSound(mrDog); self = mrDog.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- Inheritance example:
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LoudDog = Dog:new() -- 1.
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function LoudDog:makeSound()
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local s = self.sound .. ' ' -- 2.
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s = self.sound .. ' ' -- 2.
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print(s .. s .. s)
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end
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seymour = LoudDog:new() -- 3.
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seymour:makeSound() -- 'woof woof woof' -- 4.
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--------------------------------------------------------------------------------
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-- 1. LoudDog gets Dog's methods and variables.
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-- 2. self has a 'sound' key from new(), see 3.
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-- 3. Same as "LoudDog.new(LoudDog)", and converted to "Dog.new(LoudDog)" as
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-- LoudDog has no 'new' key, but does have "__index = Dog" on its metatable.
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-- Result: seymour's metatable is LoudDog, and "LoudDog.__index = Dog". So
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-- seymour.key will equal seymour.key, LoudDog.key, Dog.key, whichever
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-- 3. Same as LoudDog.new(LoudDog), and converted to
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-- Dog.new(LoudDog) as LoudDog has no 'new' key,
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-- but does have __index = Dog on its metatable.
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-- Result: seymour's metatable is LoudDog, and
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-- LoudDog.__index = LoudDog. So seymour.key will
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-- = seymour.key, LoudDog.key, Dog.key, whichever
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-- table is the first with the given key.
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-- 4. The 'makeSound' key is found in LoudDog; this is the same as
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-- "LoudDog.makeSound(seymour)".
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-- 4. The 'makeSound' key is found in LoudDog; this
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-- is the same as LoudDog.makeSound(seymour).
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-- If needed, a subclass's new() is like the base's:
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function LoudDog:new()
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local newObj = {}
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newObj = {}
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-- set up newObj
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self.__index = self
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return setmetatable(newObj, self)
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end
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--------------------------------------------------------------------------------
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----------------------------------------------------
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-- 4. Modules.
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--------------------------------------------------------------------------------
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----------------------------------------------------
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--[[ I'm commenting out this section so the rest of this script remains
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-- runnable.
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--[[ I'm commenting out this section so the rest of
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-- this script remains runnable.
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```
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```lua
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@ -359,8 +360,8 @@ local mod = require('mod') -- Run the file mod.lua.
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local mod = (function ()
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<contents of mod.lua>
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end)()
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-- It's like mod.lua is a function body, so that locals inside mod.lua are
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-- invisible outside it.
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-- It's like mod.lua is a function body, so that
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-- locals inside mod.lua are invisible outside it.
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-- This works because mod here = M in mod.lua:
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mod.sayHello() -- Says hello to Hrunkner.
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@ -368,19 +369,19 @@ mod.sayHello() -- Says hello to Hrunkner.
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-- This is wrong; sayMyName only exists in mod.lua:
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mod.sayMyName() -- error
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-- require's return values are cached so a file is run at most once, even when
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-- require'd many times.
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-- require's return values are cached so a file is
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-- run at most once, even when require'd many times.
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-- Suppose mod2.lua contains "print('Hi!')".
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local a = require('mod2') -- Prints Hi!
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local b = require('mod2') -- Doesn't print; a=b.
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-- dofile is like require without caching:
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dofile('mod2') --> Hi!
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dofile('mod2') --> Hi! (runs again, unlike require)
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dofile('mod2.lua') --> Hi!
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dofile('mod2.lua') --> Hi! (runs it again)
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-- loadfile loads a lua file but doesn't run it yet.
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f = loadfile('mod2') -- Calling f() runs mod2.lua.
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f = loadfile('mod2.lua') -- Call f() to run it.
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-- loadstring is loadfile for strings.
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g = loadstring('print(343)') -- Returns a function.
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