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https://github.com/adambard/learnxinyminutes-docs.git
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423 lines
15 KiB
Markdown
423 lines
15 KiB
Markdown
---
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language: lua
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filename: learnlua-ru.lua
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contributors:
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- ["Tyler Neylon", "http://tylerneylon.com/"]
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translators:
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- ["Max Solomonov", "https://vk.com/solomonovmaksim"]
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lang: ru-ru
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---
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```lua
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-- Два дефиса начинают однострочный комментарий.
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--[[
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Добавление двух квадратных скобок
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делает комментарий многострочным.
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--]]
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--------------------------------------------------------------------------------
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-- 1. Переменные, циклы и условия.
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--------------------------------------------------------------------------------
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num = 42 -- Все числа являются типом double.
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--[[
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Не волнуйся, 64-битные double имеют 52 бита
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для хранения именно целочисленных значений;
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точность не является проблемой для
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целочисленных значений, занимающих меньше
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52 бит.
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--]]
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s = 'walternate' -- Неизменные строки как в Python.
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t = "Двойные кавычки также приветствуются"
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u = [[ Двойные квадратные скобки
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начинают и заканчивают
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многострочные значения.]]
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t = nil -- Удаляет определение переменной t; Lua имеет мусорку.
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-- Циклы и условия имеют ключевые слова, такие как do/end:
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while num < 50 do
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num = num + 1 -- Здесь нет ++ или += операторов.
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end
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-- Условие "если":
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if num > 40 then
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print('больше 40')
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elseif s ~= 'walternate' then -- ~= обозначает "не равно".
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-- Проверка равенства это == как в Python; ok для строк.
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io.write('не больше 40\n') -- По умолчанию стандартный вывод.
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else
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-- По умолчанию переменные являются глобальными.
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thisIsGlobal = 5 -- Стиль CamelСase является общим.
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-- Как сделать локальную переменную:
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local line = io.read() -- Считывает введённую строку.
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-- Конкатенация строк использует .. оператор:
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print('Зима пришла, ' .. line)
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end
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-- Неопределённые переменные возвращают nil.
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-- Этот пример не является ошибочным:
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foo = anUnknownVariable -- Теперь foo = nil.
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aBoolValue = false
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-- Только значения nil и false являются ложными; 0 и '' являются истинными!
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if not aBoolValue then print('это значение ложно') end
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--[[
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Для 'or' и 'and' действует принцип "какой оператор дальше,
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тот и применяется". Это действует аналогично a?b:c
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операторам в C/js:
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--]]
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ans = aBoolValue and 'yes' or 'no' --> 'no'
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karlSum = 0
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for i = 1, 100 do -- Здесь указан диапазон, ограниченный с двух сторон.
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karlSum = karlSum + i
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end
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-- Используйте "100, 1, -1" как нисходящий диапазон:
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fredSum = 0
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for j = 100, 1, -1 do fredSum = fredSum + j end
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-- В основном, диапазон устроен так: начало, конец[, шаг].
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-- Другая конструкция цикла:
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repeat
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print('путь будущего')
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num = num - 1
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until num == 0
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--------------------------------------------------------------------------------
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-- 2. Функции.
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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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return fib(n - 2) + fib(n - 1)
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end
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-- Вложенные и анонимные функции являются нормой:
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function adder(x)
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-- Возращаемая функция создаётся когда adder вызывается, тот в свою очередь
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-- запоминает значение переменной 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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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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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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function bar(a, b, c)
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print(a, b, c)
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return 4, 8, 15, 16, 23, 42
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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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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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-- Trig funcs work in radians, by the way.
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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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-- 3. Tables.
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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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-- Using tables as dictionaries / maps:
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-- Dict literals have string keys by default:
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t = {key1 = 'value1', key2 = false}
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-- String keys can use js-like dot notation:
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print(t.key1) -- Prints 'value1'.
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t.newKey = {} -- Adds a new key/value pair.
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t.key2 = nil -- Removes key2 from the table.
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-- Literal notation for any (non-nil) value as key:
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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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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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-- A one-table-param function call needs no parens:
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function h(x) print(x.key1) end
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h{key1 = 'Sonmi~451'} -- Prints 'Sonmi~451'.
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for key, val in pairs(u) do -- Table iteration.
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print(key, val)
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end
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-- _G is a special table of all globals.
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print(_G['_G'] == _G) -- Prints 'true'.
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-- Using tables as lists / arrays:
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-- List literals implicitly set up int keys:
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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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--------------------------------------------------------------------------------
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-- 3.1 Metatables and metamethods.
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--------------------------------------------------------------------------------
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-- A table can have a metatable that gives the table operator-overloadish
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-- behavior. Later we'll see 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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-- This would fail:
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-- s = f1 + f2
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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.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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end
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setmetatable(f1, metafraction)
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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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-- But the next line fails since s has no metatable:
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-- t = s + s
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-- Class-like patterns given below would fix this.
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-- An __index on a metatable overloads dot lookups:
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defaultFavs = {animal = 'gru', food = 'donuts'}
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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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-- An __index value can also be a function(tbl, key) for more customized
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-- 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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-- __add(a, b) for a + b
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-- __sub(a, b) for a - b
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-- __mul(a, b) for a * b
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-- __div(a, b) for a / b
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-- __mod(a, b) for a % b
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-- __pow(a, b) for a ^ b
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-- __unm(a) for -a
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-- __concat(a, b) for a .. b
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-- __len(a) for #a
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-- __eq(a, b) for a == b
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-- __lt(a, b) for a < b
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-- __le(a, b) for a <= b
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-- __index(a, b) <fn or a table> for a.b
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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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-- 3.2 Class-like tables and inheritance.
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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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-- 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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self.__index = self -- 4.
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return setmetatable(newObj, self) -- 5.
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end
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function Dog:makeSound() -- 6.
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print('I say ' .. self.sound)
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end
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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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-- 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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-- 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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-- 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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-- 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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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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-- 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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-- 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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-- 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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-- 4. Modules.
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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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```
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```lua
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-- Suppose the file mod.lua looks like this:
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local M = {}
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local function sayMyName()
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print('Hrunkner')
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end
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function M.sayHello()
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print('Why hello there')
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sayMyName()
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end
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return M
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-- Another file can use mod.lua's functionality:
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local mod = require('mod') -- Run the file mod.lua.
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-- require is the standard way to include modules.
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-- require acts like: (if not cached; see below)
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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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-- This works because mod here = M in mod.lua:
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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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-- 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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-- 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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-- loadstring is loadfile for strings.
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g = loadstring('print(343)') -- Returns a function.
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g() -- Prints out 343; nothing printed before now.
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--]]
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```
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## References
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I was excited to learn Lua so I could make games
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with the <a href="http://love2d.org/">Love 2D game engine</a>. That's the why.
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I started with <a href="http://nova-fusion.com/2012/08/27/lua-for-programmers-part-1/">BlackBulletIV's Lua for programmers</a>.
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Next I read the official <a href="http://www.lua.org/pil/contents.html">Programming in Lua</a> book.
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That's the how.
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It might be helpful to check out the <a href="http://lua-users.org/files/wiki_insecure/users/thomasl/luarefv51.pdf">Lua short
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reference</a> on lua-users.org.
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The main topics not covered are standard libraries:
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* <a href="http://lua-users.org/wiki/StringLibraryTutorial">string library</a>
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* <a href="http://lua-users.org/wiki/TableLibraryTutorial">table library</a>
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* <a href="http://lua-users.org/wiki/MathLibraryTutorial">math library</a>
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* <a href="http://lua-users.org/wiki/IoLibraryTutorial">io library</a>
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* <a href="http://lua-users.org/wiki/OsLibraryTutorial">os library</a>
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By the way, the entire file is valid Lua; save it
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as learn.lua and run it with "lua learn.lua" !
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This was first written for tylerneylon.com, and is
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also available as a <a href="https://gist.github.com/tylerneylon/5853042">github gist</a>. Have fun with Lua!
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