Lua完美打印一个Table的方案

function print_r ( t )  
    local print_r_cache={}
    local function sub_print_r(t,indent)
        if (print_r_cache[tostring(t)]) then
            print(indent.."*"..tostring(t))
        else
            print_r_cache[tostring(t)]=true
            if (type(t)=="table") then
                for pos,val in pairs(t) do
                    if (type(val)=="table") then
                        print(indent.."["..pos.."] => "..tostring(t).." {")
                        sub_print_r(val,indent..string.rep(" ",string.len(pos)+8))
                        print(indent..string.rep(" ",string.len(pos)+6).."}")
                    elseif (type(val)=="string") then
                        print(indent.."["..pos..'] => "'..val..'"')
                    else
                        print(indent.."["..pos.."] => "..tostring(val))
                    end
                end
            else
                print(indent..tostring(t))
            end
        end
    end
    if (type(t)=="table") then
        print(tostring(t).." {")
        sub_print_r(t,"  ")
        print("}")
    else
        sub_print_r(t,"  ")
    end
    print()
end

print_r函数可以完整的打印table，并且可以清晰的打印table中嵌套table的内容。对于调试和检查程序都有很大的好处。

另外，直接使用print_r不太符合直觉，可以把函数放如table的名字空间里，如下：

table.print = print_r

这样就可以自然的使用这个函数：

table.print( myTable )

打印的结果，类似下面内容：

local myTable = {
    firstName = "Fred",
    lastName = "Bob",
    phoneNumber = "(555) 555-1212",
    age = 30,
    favoriteSports = { "Baseball", "Hockey", "Soccer" },
    favoriteTeams  = { "Cowboys", "Panthers", "Reds" }
}

table.print_r(myTable)

table: 0x7fa832d012e0 {
  [firstName] => "Fred"
  [favoriteSports] => table: 0x7fa832d012e0 {
                        [1] => "Baseball"
                        [2] => "Hockey"
                        [3] => "Soccer"
                      }
  [phoneNumber] => "(555) 555-1212"
  [favoriteTeams] => table: 0x7fa832d012e0 {
                       [1] => "Cowboys"
                       [2] => "Panthers"
                       [3] => "Reds"
                     }
  [lastName] => "Bob"
  [age] => 30
}