Lua Interface

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-- It should also be noted that this works on the Mono runtime http://www.mono-project.com on Linux.

local a = SomeType[5]
for i = 1,a.Length do
	print(i, a[i - 1]) -- .NET arrays are zero-based.
end

When using the CLR from Lua, the ordinary method of loading types and classes can seem a little verbose:

net = require "luainterface"

net.load_assembly("System.Windows.Forms")
net.load_assembly("System.Drawing")

Form = net.import_type("System.Windows.Forms.Form")
Button = net.import_type("System.Windows.Forms.Button")
Point = net.import_type("System.Drawing.Point")

local form1 = Form()
local button1 = Button()
button1.Location = Point(10, 10)

It would be nice if syntax like this could be used:

require "net"

Form = net.System.Windows.Forms.Form
Button = net.System.Windows.Forms.Button
Point = net.System.Drawing.Point

local form1 = Form()
local button1 = Button()
button1.Location = Point(10, 10)

Optionally, the .NET types can be made to appear as toplevel names:

require "net"

System = net.System

Form = System.Windows.Forms.Form
Button = System.Windows.Forms.Button
Point = System.Drawing.Point

local form1 = Form()
local button1 = Button()
button1.Location = Point(10, 10)

It should not be necessary to make every type name toplevel:

require "net"

System = net.System

local form1 = System.Windows.Forms.Form()
local button1 = System.Windows.Forms.Button()
button1.Location = System.Drawing.Point(10, 10)

Here is the method:

-- Create a metatable for our name components
local metatable = { [".NET"] = {getmetatable=getmetatable} }

-- Load LuaInterface
local g = getfenv(0)
setfenv(0, metatable[".NET"])
local init, e1, e2 = loadlib("LuaInterfaceLoader.dll", "luaopen_luainterface")
assert(init, (e1 or '') .. (e2 or ''))
init()
setfenv(0, g)

-- Lookup a .NET identifier component.
function metatable:__index(key) -- key is e.g. "Form"
    local mt = getmetatable(self)
    local luanet = mt[".NET"]

    -- Get the fully-qualified name, e.g. "System.Windows.Forms.Form"
    local fqn = ((self[".fqn"] and self[".fqn"] .. ".") or "") .. key

    -- Try to find either a luanet function or a CLR type
    local obj = luanet[key] or luanet.import_type(fqn)

    -- If key is neither a luanet function or a CLR type, then it is simply
    -- an identifier component.
    if obj == nil then
		-- It might be an assembly, so we load it too.
        luanet.load_assembly(fqn)
        obj = { [".fqn"] = fqn }
        setmetatable(obj, mt)
    end

    -- Cache this lookup
    self[key] = obj
    return obj
end

-- A non-type has been called; e.g. foo = System.Foo()
function metatable:__call(...)
    error("No such type: " .. self[".fqn"], 2)
end

-- This is the root of the .NET namespace
net = { [".fqn"] = false }
setmetatable(net, metatable)

-- Preload the mscorlib assembly
net.load_assembly("mscorlib")

return nil