Question

我在C ++中有这段代码，我想知道如何编写一些替换Lua中的switch语句的代码，因为我遇到很多问题，我需要使用这个语句。

   int choice;
do// loop
{
      cout<<"\n >>> The General Menu <<< \n";
      cout << endl;
    cout<< " press (1) to Add    "<<endl;
    cout<< " press (2) to Save   "<<endl;
    cout<< " press (3) to Quit " << endl;
    cout<< endl;
      cout<< "Enter your choice please (1/2/3): ";
    cin>>choice;

    switch(choice)
    {
        case 1: 
            add();
            break;
        case 2:
            save();
            break;

        default:
            cout<<" The program has been terminated "<<endl;
           cout<<" Thank you! \n";          
    }   
} while (choice != 3);

} 该语句已在do..while循环中使用。

Answer 1

一般来说，如果你想在Lua中使用switch语句，你应该做的是构建一个表。对于choice的简单情况（可能是1,2或失败），只需要一些条件的简单if语句就足够了。对于更复杂的情况，应使用函数表：

local c_tbl =
{
  [1] = add,
  [2] = save,
}

local func = c_tbl[choice]
if(func) then
  func()
else
  print " The program has been terminated."
  print " Thank you!";
end

您可以使用词法作用域允许表中的函数能够访问局部变量，就像代码是内联编写一样。

Answer 2

的Lua：

if choice == 1
then add()
elseif choice == 2
then save()
else print "The program has been terminated\nThank you!"
end

Answer 3

试试这个(click here to run the script in a Lua compiler)，希望代码不言自明;-)和

类似于伪代码格式.. !!

print("enter your choice : ")
mychoice = io.read()

switch = function (choice)
  -- accepts both number as well as string
  choice = choice and tonumber(choice) or choice     -- returns a number if the choic is a number or string. 

  -- Define your cases
  case =
   {
     [1] = function ( )                              -- case 1 : 
             print("your choice is Number 1 ")       -- code block
     end,                                            -- break statement

     add = function ( )                              -- case 'add' : 
             print("your choice is string add ")     -- code block
     end,                                            -- break statement

    ['+'] = function ( )                             -- case '+' : 
             print("your choice is char + ")         -- code block
     end,                                            -- break statement

     default = function ( )                          -- default case
             print(" your choice is din't match any of those specified cases")   
     end,                                            -- u cant exclude end hear :-P
   }

  -- execution section
  if case[choice] then
     case[choice]()
  else
     case["default"]()
  end

end
-- Now you can use it as a regular function. Tadaaa..!!
switch(mychoice)

Answer 4

另一个版本的切换器（没有将表初始化为变量）：

local case=2;
local result=({[1]="case1", [2]="case2", 3="case3"})[case];
print (result); --> case2

Answer 5

我遇到了带有不同参数的函数的问题-其他答案无法很好地解决这些问题。
我用匿名函数解决了这个问题。

'use strict';

const e = React.createElement;

class LikeButton extends React.Component {
  constructor(props) {
    super(props);
    this.state = { liked: false };
    this.state={checked: false}

  //this.handleCheckedChange = this.handleCheckedChange.bind(this);
  this.handleSubmit = this.handleSubmit.bind(this);
  this.formContent = this.display1();
  }

  handleSubmit(event) {
    alert('Your information is: ' + JSON.stringify(this.formContent) + " " + "Please Make Sure To Select From One of The Vacation Options and Activities From Below");
  
    event.preventDefault();}

  

  NumberList1(props) {
    let listItems = React.createElement("p", {key: props.id}, props.item.text, React.createElement("input", {
      type: "checkbox",
      value: "1",
      onChange: () => this.setState({checked: true}),
      defaultChecked: false
    }))
    
    return (
      listItems      
    )
  }

  display1(){
      
    let props = [{id: 0, text: "City Tours", completed: false}, 
    {id: 1, text: "Sports", completed: false}, 
    {id: 2, text: "Cycling", completed: false}, 
    {id: 3, text: "Museums", completed: false}, 
    {id: 4, text: "Boating", completed: false}];  
    let listItems = props.map((item) => this.NumberList1({
      key: props.id, 
      item: item})); 

      return(React.createElement("div", {}, listItems));
  }
        

  render() {
   

    //if(this.state.liked == true){
    
      //;}
    
    
      //'button',{ onClick: () => this.setState({ liked: true }) },"New Zealand",

    return (React.createElement("form", {onSubmit: this.handleSubmit, action: 'http://localhost/test.php', method: "get",
    className: "todo-list"
  },"Select Activities From Below", (this.formContent),React.createElement("br", {}), 
  React.createElement("input", {type:"submit", value: "Submit"}), 
  React.createElement("input", {type:"reset", value: "Reset"})))
}

}

 const domContainer = document.getElementById("new");

 ReactDOM.render(
   (e(LikeButton)),
   domContainer);

Answer 6

如果你想将switch作为一个可调用的函数，你可以使用一些有趣的回调功能：

（以下示例是基于变量类型的switch语句，但您可以将表索引转换为您要测试它的任何内容。只需将switch函数的return语句更改为不测试类型（case））

（这实际上是一个懒惰的表查找，很像Python的字典功能，但每个元素都是一个函数）

#!/usr/bin/lua
-- Callback switch statement:
local function switch(a, case)
  -- Local variable instead of function(a) on every case:
  local value = a
  -- Cases list:
  local switchcase = {}

  -- Cases:
  switchcase["string"] = function()
    return (tostring(value) .. " is a string")
  end

  switchcase["number"] = function()
    return tostring(value .. " is a number")
  end

  switchcase["boolean"] = function()
    return (tostring(avalue) .. " is a boolean")
  end

  return switchcase[type(case)](a)
end

local value = 5
print(switch(value,value)) --> 5 is a number

local value = "test"
print(switch(value,value)) --> test is a string

local value = true
print(switch(value,value)) --> true is a boolean

我不知道这个代码的性能与上面给出的两个答案相比，但是使用局部变量应该使它足够快以便重复使用。如果在全局范围内进行切换功能，它可以成为项目使用的标准功能。

Answer 7

这是另一个使用loadstring（）和表查找的有趣方法。

switch = function(cases,args)
  if (cases[args] == nil) then return args else return assert(loadstring ('return ' .. cases[args]))() end
end

local case = 2

local result = switch({
  [1] = "2^" .. case,
  [2] = string.format("2^%i",case),
  [3] = tostring(2^case)
},
case
)
print(result) --> 4

使用此方法有点危险，因为loadstring（）类似于Python的eval（）函数。

我发现写＆＃34; function（x）＆＃34;在Lua wiki提供的示例中的每个案例中。这是一个很好的方式。

＆＃34;默认＆＃34;案例是＆＃34; return args＆＃34;功能的一部分。

Answer 8

我使用以下代码：

while true do local tmpswitch1 = exp ; --[[ switch <exp> do ]]
    if tmpswitch1 == exp1 then --[[ case <exp1> : ]]
        -- do something
        break
    end ;if tmpswitch1 == exp2 then --[[ case <exp2> : ]]
        -- do something
        break
    end ; --[[ default : ]]
        -- do something
break ; end --[[ switch tmpswitch1 ]]

Answer 9

虽然最简单的方法是创建一个以事例为索引的表，并以函数作为元素，这是最快的方法，但我提出的这种解决方案使IMO具有更好的代码可读性：

function switch(element)
  local Table = {
    ["Value"] = element,
    ["DefaultFunction"] = nil,
    ["Functions"] = {}
  }
  
  Table.case = function(testElement, callback)
    Table.Functions[testElement] = callback
    return Table
  end
  
  Table.default = function(callback)
    Table.DefaultFunction = callback
    return Table
  end
  
  Table.process = function()
    local Case = Table.Functions[Table.Value]
    if Case then
      Case()
    elseif Table.DefaultFunction then
      Table.DefaultFunction()
    end
  end
  
  return Table
end

示例用法：

switch(Player:GetName())
  .case("Kate", function() print("This player's name rhymes with Fate")end)
  .case("Tod", function() print("This player's name rhymes with Cod") end)
  .default(function() print("This player's name is not Kate or Tod") end)
  .process()

Lua语言中switch语句的替代方法是什么？

9 个答案: