Lua Ropes

wiki

Lua Ropes

由於字串在 Lua 中為不可變物件，因此避免不必要建立字串非常重要。許多時候程式會操控字串以建立某些文字輸出。其中一項策略是避免建立中間字串，並以正確順序輸出最後文字的各個部分。適當的資料類型為繩[1]，其中

 rope ::= string | list of rope 

do
  local function walk(x,f)
    local typ, ok, bad = type(x),true
    local errmsg = "bad type (%s), %s"
    if typ == "string" then return pcall(f,x)
    elseif typ == "table" then
      local i,n = 1,#x
      while ok and i <= n do
        ok,bad = walk(x[i],f)
        i = i+1
      end -- while
      return ok,bad
    else
      bad = errmsg:format(typ,typ and "" or "something undefined?")
      return nil,bad
    end -- if
  end -- function

  local mt = {
    push = function (self,x)
      local function f(y)
        if y and type(y) ~= "function" then
          self[#self + 1] =y
          return f
        elseif y then
          return function (z)
            return f(y(z))
          end -- function
        end -- if
      end -- function y
      return f(x)
    end; -- function push
    walk = walk;
    flatten = function(self)
      local o = {}
      local f = function (x) o[#o + 1] = x end -- function
      self:walk(f)
      return table.concat(o)
    end; -- function
  }

  function rope()
    return setmetatable({}, {__index = mt})
  end -- function
end -- do

t,x = rope(),rope()
t:push (string.upper) "m" "r" (string.char) (32) "Smith" ;
x:push [[ Good ]] [[morning]];
t:push (x)
t:walk(io.write) --> Mr Smith Good morning
print(t:flatten()) --> Mr Smith Good morning