NeoLua (Lua for the .NET Dynamic Language Runtime)

NeoLua (Lua for the .NET Dynamic Language Runtime)

neolithos, 17 Nov 2014 Apache 47.6K 1.3K 93

 

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NeoLua implements Lua as a .NET dynamic language.

Link to binaries 0.9.9

Link to source code 0.9.9

Download NeoSpeed.zip – 407.3 KB

Introduction

NeoLua is an implementation of the Lua language that totally started from scratch. Currently, the implementation is on the level of Lua 5.2 (http://www.lua.org/manual/5.2/manual.html) with many parts of Lua 5.3. The goal is to follow the reference of the C-Lua implementation and combine this with the full .NET Framework support. That means it should be easy to call .NET functions/classes/interfaces/events from Lua and it should be easy to access variables and functions of Lua from a .NET language (e.g. C#, VB.NET, …).

NeoLua is implemented in C# and uses the Dynamic Language Runtime. At the time, NeoLua has only one dependency to the .NET framework 4 and it also works under the current mono framework.

Background

The idea of NeoLua was born because I needed Lua as a scripting language in a service application. In the first release, I used LuaInterface. But it turned out that it is really hard to use LuaInterface as a bridge between .NET and C-Lua correctly.

I got a lot of memory leaks! During debugging, I discovered that I did not de-reference the Lua variables correctly and learned that to do this right is really hard.

Principles

What NeoLua is Useful For

Outsource the logic of your application into scripts

Structuring of logic

Build a dynamic configuration system, with functions and variables

As a formula parser

So, this could be reliable partner for your compiled .NET application or engine (e.g. Game Engines).

What I Did Not Have In Mind

Compiling libraries

Standalone applications

Advantages of NeoLua

Dynamic access between Lua script and the host application/.NET framework and vice-versa.

NeoLua is based on the DLR. So you get compiled code that is collectable and well-optimized.

It is possible to write strict scripts. Runtime speed is like e.g. C#.

It is compatible with the .NET world (e.g. C#, VB.NET, IronPython, …).

Full and easy access to the .NET framework or your own libraries (with no stub code).

A .NET Framework Garbage Collector that is well-tested and very fast.

Pure IL (x86,x64 support)

Drawbacks of NeoLua

It is not 100% compatible with Lua.

No deployment of precompiled scripts.

Drawbacks of Bridges to C-lua, that are Solved with NeoLua

With C-Lua, you have to deal with two memory managers and so you have to marshal all data between these two worlds. That takes time and there are a lot of pitfalls to get memory leaks.

C-Lua interprets its own bytecode. The code is not compiled to machine code.

Hello World

To get started with NeoLua is very easy. At first, you have to add a reference to the Neo.Lua-Assembly. There are two ways to get NeoLua. First, download it from neolua.codeplex.com.

The second way is to use the nuget package.

Next, create an instance of the Neo.IronLua.Lua (called Lua-Script-Engine) and get a fresh environment to execute Lua code.

Here is an example that prints "Hello World!" in the debug output:

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using Neo.IronLua;

namespace Test

{

  public static class Program

  {

    public static void Main(string[] args)

    {

      // Create the Lua script engine

      using (Lua l = new Lua())

      {

        // create a Lua script environment (global)

        var g = l.CreateEnvironment();

        // run a chunk, first the code, than the name of the code

        g.DoChunk("print('Hello World!');", "test.lua");

      }

    }

  }

}

Playing with NeoLua

LuaCmd is a interactive program to test NeoLua. Check it out. Just write Lua code and execute it with a empty line.

Running Lua-Snippets

To run a small snippet, just execute it via DoChunk. Scripts can have parameters, like in example a and b. Every script can return values. The return value of scripts are always LuaResult of objects, because in Lua, it is possible to return more than one result.

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using (Lua l = new Lua())

{

    var g = l.CreateEnvironment();

    var r = g.DoChunk("return a + b", "test.lua",

      new KeyValuePair<string, object>("a", 2),

      new KeyValuePair<string, object>("b", 4));

    Console.WriteLine(r[0]);

}

Because NeoLua is a dynamic language, there is also a way to do it dynamically. Also LuaResult has a dynamic interface.

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using (Lua l = new Lua())

{

    dynamic g = l.CreateEnvironment();

    dynamic dr = dg.dochunk("return a + b", "test.lua", "a", 2, "b", 4);

    Console.WriteLine((int)dr);

}

Values and Types

NeoLua is not a dynamically typed language, it just looks like it is. Variables always have a type (at least System.Object).

NeoLua supports all CLR types. If there is type conversion necessary, it is done automatically. Dynamic types are also supported.

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local a = "5"; — a string is assigned to a local variable of the type object

local b = {}; — object assigned with an empty table 

b.c = a + 8; — the variable "a" is converted into an integer and assigned to the dynamic member of a table

A nice feature of NeoLua is strict typing. But more in a later section.

Working with Globals

The environment is a special Lua table. Set or get the variables on the environment and they are accessible in the script-code as global variables.

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using (Lua l = new Lua())

{

    var g = l.CreateEnvironment();

    dynamic dg = g;

    

    dg.a = 2; // dynamic way to set a variable

    g["b"] = 4; // second way to access variable

    g.DoChunk("c = a + b", "test.lua");

    Console.WriteLine(dg.c);

    Console.WriteLine(g["c"]);

}

Working with LuaTables

The implementation of NeoLua supports the dynamic class LuaTable. This class is used by the script-code as it is. The next examples hopefully show the idea.

Member

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using (Lua l = new Lua())

{

  dynamic dg = l.CreateEnvironment();

  dg.t = new LuaTable();

  dg.t.a = 2;

  dg.t.b = 4;

  dg.dochunk("t.c = t.a + t.b", "test.lua");

  Console.WriteLine(dg.t.c);

}

Index Access

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using (Lua l = new Lua())

{

  dynamic dg = l.CreateEnvironment();

  dg.t = new LuaTable();

  dg.t[0] = 2;

  dg.t[1] = 4;

  dg.dochunk("t[2] = t[0] + t[1]", "test.lua");

  Console.WriteLine(dg.t[2]);

}

Functions

Defining a function feels natural. It is basically a delegate that is assigned to a member.

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using (Lua l = new Lua())

{

  dynamic dg = l.CreateEnvironment();

  dg.myadd = new Func<int, int, int>((a, b) => a + b); // define a new function in c#

  dg.dochunk("function Add(a, b) return myadd(a, b) end;", "test.lua"); // define a new function in lua that calls the C# function

  Console.WriteLine((int)dg.Add(2, 4)); //call the Lua function

  var f = (Func<object,>)dg.Add;// get the Lua function

  Console.WriteLine(f(2, 4).ToInt32());

}

Methods (Host Application)

The next example defines three members.

a , b are members, they are holding an ordinary integer. And add is holding a function, but this definition is not a method. Because if you try to call the function like a method in e.g. C#, it will throw a NullReferenceException. You must always pass the table as a first parameter to it. To declare a real method, you have to call the explicit method DefineMethod. Lua does not care about the difference, but C# or VB.NET do.

 

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using (Lua l = new Lua())

{

  dynamic dg = l.CreateEnvironment();

  dg.t = new LuaTable();

  dg.t.a = 2;

  dg.t.b = 4;

  

  dg.t.add = new Func<dynamic, int>(self => 

    {

      return self.a + self.b;

    });

  ((LuaTable)dg.t).DefineMethod("add2", (Delegate)dg.t.add);

  Console.WriteLine(dg.dochunk("return t:add()", "test.lua")[0]);

  Console.WriteLine(dg.dochunk("return t:add2()", "test.lua")[0]);

  Console.WriteLine(dg.t.add(dg.t));

  Console.WriteLine(dg.t.add2());

}

Methods (Lua)

add is a normal function, created from a delegate.

add1 is declared as a function.

add2 is a method, that is created from a delegate. Be aware that a delegate definition doesn't know anything about the concept of methods, so you have to declare the self parameter.

add3 shows a method declaration.

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using (Lua l = new Lua())

{

  dynamic dg = l.CreateEnvironment();

  LuaResult r = dg.dochunk("t = { a = 2, b = 4 };" +

    "t.add = function(self)" +

    "  return self.a + self.b;" +

    "end;" +

    "function t.add1(self)" +

    "  return self.a + self.b;" +

    "end;" +

    "t:add2 = function (self)" +

    "  return self.a + self.b;" +

    "end;" +

    "function t:add3()" +

    "  return self.a + self.b;" +

    "end;" +

    "return t:add(), t:add2(), t:add3(), t.add(t), t.add2(t), t.add3(t);", 

    "test.lua");

  Console.WriteLine(r[0]);

  Console.WriteLine(r[1]);

  Console.WriteLine(r[2]);

  Console.WriteLine(r[3]);

  Console.WriteLine(r[4]);

  Console.WriteLine(r[5]);

  Console.WriteLine(dg.t.add(dg.t)[0]);

  Console.WriteLine(dg.t.add2()[0]);

  Console.WriteLine(dg.t.add3()[0]);

}

Metatables

If you define a metatable on a table, you can also use this in the host language like C#.

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using (Lua l = new Lua())

{

  dynamic g = l.CreateEnvironment();

  dynamic r = g.dochunk(String.Join(Environment.NewLine,

    "tm = {};",

    "tm.__add = function (t, a) return t.n + a; end;",

    "t = { __metatable = tm, n = 4 };",

    "return t + 2"));

  LuaTable t = g.t;

  Console.WriteLine((int)r);

  Console.WriteLine(t + 2);

}

And vice versa.

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using (Lua l = new Lua())

{

  dynamic g = l.CreateEnvironment();

  LuaTable t = new LuaTable();

  t["n"] = 4;

  t.MetaTable = new LuaTable();

  t.MetaTable["__add"] = new Func<LuaTable, int, int>((_t, a) => (int)(_t["n"]) + a);

  g.t = t;

  dynamic r = g.dochunk("return t + 2");

  Console.WriteLine((int)r);

  Console.WriteLine(t + 2);

}

NeoLua does not support setting metatables on userdata, because there is no definition of userdata. But NeoLua uses the operator definitions of a type. That is the same result.

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public class ClrClass

{

  private int n = 4;

  public static int operator +(ClrClass c, int a)

  {

    return c.n + a;

  }

}

using (Lua l = new Lua())

{

  dynamic g = l.CreateEnvironment();

  g.c = new ClrClass();

  Console.WriteLine((int)g.dochunk("return c + 2;"));

}

Classes/Objects

To create a class, you have to write a function that creates a new object. The function is by definition the class and the result of the function is the object.

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using (Lua l = new Lua())

{

  dynamic dg = l.CreateEnvironment();

  dg.dochunk("function classA()" +

    "  local c = { sum = 0 };" +

    "  function c:add(a)" +

    "    self.sum = self.sum + a;" +

    "  end;" +

    "  return c;" +

    "end;", "classA.lua");

  dynamic o = dg.classA()[0];

  o.add(1);

  o.add(2);

  o.add(3);

  Console.WriteLine(o.sum);

}

Explicit Typing

A nice feature of NeoLua is its use of strict typing. That means you can give your local variables or parameters a strict type (like in C#). A big advantage of this feature is that the parser can do a lot of stuff during compile time. This will short-cut a lot of the dynamic parts they are normally in a NeoLua script (so the script should run pretty fast).

Globals and Tables cannot have typed dynamic members, they are by implementation always of the type object. One exception is the explicit declarion in a .net class that is inherited from LuaTable.

Example without explicit type:

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// create a new instance of StringBuilder

local sb = clr.System.Text.StringBuilder();

sb:Append('Hello '):Append('World!');

return sb:ToString();

The script will be translated to something like this:

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object sb = InvokeConstructor(clr["System"]

["Text"]["StringBuilder"], new object[0]);

InvokeMethod(InvokeMethod(sb, "Append", new string[]

{ "Hello " }), "Append", new string[]{ "World!"});

return InvokeMethod(sb, "ToString", new object[0]);

The code is not the exact code that gets executed, in reality it is a litte bit more complicated, but way more efficient (e.g. Append will only resolve once during runtime, not twice like in this example). If you are interested in how this is done, I can recommend reading the documentation of the DLR.

Same example with strict type:

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// define a shortcut to a type, this line is only seen by the parser

const StringBuilder typeof clr.System.Text.StringBuilder;

// create a new instance of StringBuilder

local sb : StringBuilder = StringBuilder();

sb:Append('Hello '):Append('World!');

return sb:ToString();

This script is compiled like it will be done from e.g. C#:

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StringBuilder sb = new StringBuilder();

sb.Append(("Hello (").Append(("World!(");

return sb.ToString();

Types are very useful to create functions with a strict signature.

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using (Lua l = new Lua())

{

  dynamic dg = l.CreateEnvironment();

  dg.dochunk("function Add(a : int, b : int) : int return a + b; end;", "test.lua");

  Console.WriteLine((int)dg.Add(2, 4)); // the cast is needed because of the dynamic call

  var f = (Func<int,int,int>)dg.Add;

  Console.WriteLine(f(2, 4));

}

Compiled Code

Executing a script in NeoLua always means that it will be compiled and the result will be executed. If the result e.g. is a function and you call the function, it is not interpreted.

If you want to use a script multiple times, pre-compile the script-code with CompileChunk and run it on different environments. That saves compile time and memory.

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using (Lua l = new Lua())

{

    LuaChunk c = l.CompileChunk("return a;", "test.lua", false);

    var g1 = l.CreateEnvironment();

    var g2 = l.CreateEnvironment();

    g1["a"] = 2;

    g2["a"] = 4;

    Console.WriteLine((int)(g1.DoChunk(c)[0]) + (int)(g2.DoChunk(c)[0]));

}

The third parameter of the CompileChunk function decides if NeoLua should create a Dynamic-Function (false) or Runtime-Function (true). Dynamic functions are available for garbage collection, but they are not debuggable. They are the most efficient choice for small code blocks. A runtime function is compiled in a dynamic assembly in a dynamic type. The assembly/type/function is discarded when the script engine (Lua-Class) is disposed. Runtime-Functions are a good choice for scripts – they are big, often used and need debug information.

Lambda Support

A delegate that is generated by this function has no debug information and no environment. It is not allowed to use global variables or Lua functions/libraries in the code. Only the CLR package is useable. It is always compiled as a dynamic function.

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using (Lua l = new Lua())

{

  var f = l.CreateLambda<Func<double, double>>("f", "return clr.System.Math:Abs(x) * 2", "x");

  Console.WriteLine("f({0}) = {1}", 2, f(2));

  Console.WriteLine("f({0}) = {1}", 2, f(-2));

}

.NET

To access the .NET Framework classes, there is a package that is called clr. This package references namespaces and classes.

This example shows how to call the static String.Concat function:

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function a()

  return 'Hello ', 'World', '!';

end;

return clr.System.String:Concat(a());

Behind clr is the class LuaType, that tries to give access to classes, interfaces, methods, events and members in the most efficient way.

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— Load Forms

clr.System.Reflection.Assembly:Load("System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089");

local Forms = clr.System.Windows.Forms; — create a local variable with a namespace

local iClicked : int = 0;

Forms.Application:EnableVisualStyles(); — call a static method

do (frm, cmd = Forms.Form(), Forms.Button()) — create a from and button in a using block

    frm.Text = 'Hallo Welt!';

    cmd.Text = 'Click';

    cmd.Left = 16;

    cmd.Top = 16;

    cmd.Click:add( — add a event the counter part is 'remove'

        function (sender, e) : void

          iClicked = iClicked + 1;

      Forms.MessageBox:Show(frm, clr.System.String:Format('Clicked {0:N0} times!', iClicked), 'Lua', Forms.MessageBoxButtons.OK, Forms.MessageBoxIcon.Information);

        end);

    frm.Controls:Add(cmd);

    Forms.Application:Run(frm);

end;

A nice example of what is possible:

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local writeLine = clr.System.Console.WriteLine;

writeLine('Calc:');

writeLine('{0} + {1} = {2}', 2, 4, 6);

writeLine();

But it is more efficient to use the member call clr.System.Console:WriteLine(). That's because NeoLua creates an instance of the LuaOverloadedMethod-Class to manage the methods behind in the example above.

This is a point you should always have in mind when you use getmember (.) on none .NET members. Classes, interfaces return LuaType. Methods/functions return LuaOverloadedMethod or LuaMethod. And events return LuaEvent.

Complex Example

This example reads Lua script files and executes them once. The example shows how to compile a script and catch exceptions and how to retrieve the stack trace. The stack trace can only be retrieved if the script is compiled with debug information. To turn this switch on, set the second parameter of CompileChunk to true.

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using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Reflection;

using System.Threading;

namespace Neo.IronLua

{

  public static class Program

  {

    public static void Main(string[] args)

    {

      using (Lua l = new Lua())

      {

        // create an environment that is associated with the Lua scripts

        dynamic g = l.CreateEnvironment();

        // register new functions

        g.print = new Action<object[]>(Print);

        g.read = new Func<string,>(Read);

        foreach (string c in args)

        {

          using (LuaChunk chunk = l.CompileChunk(c, true)) // compile the script with 

          // debug information which is needed for a complete stack trace

            try

            {

              object[] r = g.dochunk(chunk); // execute the chunk

              if (r != null && r.Length > 0)

              {

                Console.WriteLine(new string('=', 79));

                for (int i = 0; i < r.Length; i++)

                  Console.WriteLine("[{0}] = {1}", i, r[i]);

              }

            }

            catch (TargetInvocationException e)

            {

              Console.ForegroundColor = ConsoleColor.DarkRed;

              Console.WriteLine("Exception: {0}", e.InnerException.Message);

              LuaExceptionData d = LuaExceptionData.GetData(e.InnerException); // get stack trace

              Console.WriteLine("StackTrace: {0}", d.GetStackTrace(0, false));

              Console.ForegroundColor = ConsoleColor.Gray;

            }

        }

      }

    } // Main

    private static void Print(object[] texts)

    {

      foreach (object o in texts)

        Console.Write(o);

      Console.WriteLine();

    } // proc Print

    private static string Read(string sLabel)

    {

      Console.Write(sLabel);

      Console.Write(": ");

      return Console.ReadLine();

    } // func Read

  }

}

The Lua-script is as follows:

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local a, b = tonumber(read("a")), tonumber(read("b"));

function PrintResult(o, op)

    print(o .. ' = ' .. a .. op .. b);

end;

PrintResult(a + b, " + ");

PrintResult(a – b, " – ");

PrintResult(a * b, " * ");

PrintResult(a / b, " / ");

Performance

I compared the performance to the LuaInterface project.

Not pre-compiled:

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Empty               : LuaInterface    0,7 ms    NeoLua    2,0 ms   0,358

Sum                 : LuaInterface    0,2 ms    NeoLua    0,3 ms   0,581

Sum_strict          : LuaInterface    0,3 ms    NeoLua    0,0 ms  12,500

Sum_echo            : LuaInterface    2,2 ms    NeoLua    1,4 ms   1,586

String              : LuaInterface    2,0 ms    NeoLua    0,2 ms  11,941

String_echo         : LuaInterface    5,0 ms    NeoLua    2,0 ms   2,518

Delegate            : LuaInterface    2,1 ms    NeoLua    1,0 ms   2,099

StringBuilder       : LuaInterface    3,5 ms    NeoLua    0,4 ms   8,262

CallStd             : LuaInterface    4,0 ms    NeoLua    4,2 ms   0,952

TableIntSet         : LuaInterface    1,8 ms    NeoLua    2,4 ms   0,721

TableIntGet         : LuaInterface   96,3 ms    NeoLua    8,7 ms  11,021

TableVsList         : LuaInterface    2,8 ms    NeoLua    7,5 ms   0,373

TableString         : LuaInterface   34,4 ms    NeoLua   36,5 ms   0,941

What this table shows is that they are more complex and more often you have to interact with the .NET Framework NeoLua gains a benefit over the compile overhead.

The next table shows the results with pre-compiled scripts.

Pre compiled:

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Empty               : LuaInterface    0,0 ms    NeoLua    0,0 ms     NaN

Sum                 : LuaInterface    0,0 ms    NeoLua    0,1 ms   0,333

Sum_strict          : LuaInterface    0,0 ms    NeoLua    0,0 ms     NaN

Sum_echo            : LuaInterface    1,6 ms    NeoLua    0,3 ms   4,727

String              : LuaInterface    1,2 ms    NeoLua    0,6 ms   2,000

String_echo         : LuaInterface    3,8 ms    NeoLua    0,7 ms   5,846

Delegate            : LuaInterface    1,5 ms    NeoLua    0,3 ms   5,654

StringBuilder       : LuaInterface    2,8 ms    NeoLua    0,0 ms  275,00

CallStd             : LuaInterface    3,3 ms    NeoLua    3,3 ms   1,006

TableIntSet         : LuaInterface    1,2 ms    NeoLua    1,7 ms   0,704

TableIntGet         : LuaInterface   94,1 ms    NeoLua    3,9 ms  23,876

TableVsList         : LuaInterface    2,3 ms    NeoLua    1,9 ms   1,214

TableString         : LuaInterface   30,4 ms    NeoLua   33,7 ms   0,903

Pre compiled (debug):

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Empty               : LuaInterface    0,0 ms    NeoLua    0,0 ms     NaN

Sum                 : LuaInterface    0,0 ms    NeoLua    0,1 ms   0,429

Sum_strict          : LuaInterface    0,0 ms    NeoLua    0,0 ms     NaN

Sum_echo            : LuaInterface    1,5 ms    NeoLua    0,4 ms   4,108

String              : LuaInterface    1,2 ms    NeoLua    0,4 ms   3,105

String_echo         : LuaInterface    4,0 ms    NeoLua    0,7 ms   5,812

Delegate            : LuaInterface    1,5 ms    NeoLua    0,3 ms   5,179

StringBuilder       : LuaInterface    2,7 ms    NeoLua    0,0 ms  90,667

CallStd             : LuaInterface    3,3 ms    NeoLua    3,2 ms   1,022

TableIntSet         : LuaInterface    1,2 ms    NeoLua    1,8 ms   0,670

TableIntGet         : LuaInterface   94,6 ms    NeoLua    4,3 ms  22,056

TableVsList         : LuaInterface    2,2 ms    NeoLua    2,1 ms   1,077

TableString         : LuaInterface   30,8 ms    NeoLua   34,1 ms   0,903

These values show that NeoLua is strong in repetitive tasks and interacting with the framework. E.g. in game engines or service application, these attributes should be interesting.

Parts That Are Not Implemented

Not all Lua functionality is implemented yet, and some parts may be never be implemented. However, most parts of the Lua reference work just fine.

Things that might be implemented in the future:

Hex representation for doubles

Missing runtime parts

Debugging (hard)

Things that most likely will never be implemented:

Working with upvalues

Lua-Byte-Code support

Resources

NeoLua is hosted on CodePlex: neolua.codeplex.com. There you can find the releases and a forum there.

The source is hosted on GitHub: https://github.com/neolithos/neolua

Changes

0.9.9:

New: Manipulating closures/upvalues

New: TraceLine debugging

New: Array initializer

New: Support for extension methods

Chg: chunks can run on LuaTable's

Chg: total rewrite of lua table (speed, size, combatiblity)

Chg: Redesign for the c#/vb.net/lua operators

Chg: RtInvoke can invoke all what is callable, now

Chg: Correction of the arithmetic (it is not full compatible to Lua, but compatible to .net)

Chg: Class part for lua table

0.8.18:

New: rewrite of table package

New: Lexer is public, now

Bug fixing

0.8.17:

Added: require

Bug fixing

0.8.12:

Bug fixing

0.8.9:

Changed: Redesign type system (LuaType, LuaMethod, LuaEvent)

Added: Strict parsing, when it is possible

Added: Operator support

Added: Metatable support

Added: More units tests

Bug fixing

0.8.2:

Add: coroutine package

Add: io package

Next Steps

In the next months, I will stabilize the language before I introduce new features. I hope I get a lot of bug reports. After this, I will investigate debugging/tracing for NeoLua, maybe with the support of the debug package.

License

This article, along with any associated source code and files, is licensed under The Apache License, Version 2.0

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