[LUA] Chap 5. Function

[예제]

function add_(a)
  local sum = 0
  for i = 1, #a do
    sum = sum + a[i]
  end
  return sum
 end

 function f(a, b) print(a, b) end

 f(3)
 f(3, 4)
 f(3, 4, 5)

 count = 0

 function incCount(n)
  n = n or 1 --default of n is 1
  count = count + n
 end

 --#mutiple return
 s, e = string.find("hello Lua users", "Lua")
 print(s, e) --return start point, end point

 function maximum(a)
  local mi = 1    -- index of maximum value
  local m = a[mi] -- maximum value
  for i = 1, #a do
    if a[i] > m then
      mi = i; m = a[i]
    end
  end
  return m, mi
 end

 print(maximum({8,10,23,12,5}))

 --다형성 Polymorphism
 function foo0() end
 function foo1() return "a" end
 function foo2() return "a", "b" end
 print(foo2(), 1)
 print(foo2() .. "x")

 t = {foo0()} -- t = {}
 t = {foo1()} -- t = {"a"}
 t = {foo2()} -- t = {"a","b"}
 t = {foo0(), foo2(), 4} -- t = {nil, "a", 4}

 function foo(i)
  if i == 0 then return foo0()
  elseif i == 1 then return foo1()
  elseif i == 2 then return foo2()
  end
 end

 print(foo(0))
 print(foo(1))
 print(foo(2))
 print(foo(3))

 print((foo0()))
 print((foo1()))
 print((foo2()))

 --caution : foo2() != (foo2())     foo2() -> "a", "b"   (foo2()) -> "a"


 --CAUTION : before LUA 5.1 -> unpack, after LUA 5.2 -> table.unpack

 print(table.unpack{10,20,30})
 a, b = table.unpack{10,20,30}


 --Recursion
 function unpack(t, i, n)
  i = i or 1
  n = n or #t
  if i <= n then
    return t[i], unpack(t, i+1, n)
  end
 end

 function add(...) -- varang expression
  local s = 0
  for i, v in ipairs{...} do -- (...) means variable factor
    s = s + v
  end
  return s
 end

 print(add(3, 4, 10, 25, 12))

 function id(...)
  return ...
 end --return all factor


 function foo10(...)
  print("calling foo:", ...)
  return foo(...)
 end

 function fwrite(fmt, ...)
  return io.write(string.format(fmt,...))
 end

 -- table.pack is valid after LUA 5.2
 -- using table.pack, finding nil
 function nonils(...)
  local arg = table.pack(...)
  for i = 1, arg.n do
    if arg[i] == nil then return false end
  end
  return true
 end --if table has nil, return false. if not, return true.

 print(nonils(2, 3, nil))
 print(nonils(2, 3))
 print(nonils())
 print(nonils(nil))

 function rename(arg)
  return os.rename(arg.old,arg.new)
 end



 --named parameter
 function Window(options)
  --below is mendatory
  if type(options.title) ~= "string" then
    error("no title")
  elseif type(options.width) ~= "number" then
    error("no width")
  elseif type(options.height) ~= "number" then
    error("no height")
  end

  --below is not mendatory
 
  _Window(options.title,
          options.x or 0, --default is 0
          options.y or 0, --default is 0
          options.width, options.height,
          options.bacground or "white", --default is white
          options.border --default is nil       
          )
 end

 --w = Window{x=0, y=0, width=300, height=200, title="Lua", background="blue", border = true}

[결과]
3 nil
3 4
3 4
7 9
23 3
a 1
ax
a
a b
nil
a
a
10 20 30
54
false
true
true
false