Dealing with Arrays and .NET Collections

Array values are very common argument types, and are often returned by functions. LuaInterface provides a convenient index notation for accessing the values, but note that the index runs from zero to Length-1!

Creating an array of strings is easy. Use the type name followed by the size in square brackets - this is consistent with the C# syntax.

ss = String[3]

ss[0] = "one"

ss[1] = "two"

ss[2] = "three"

However, note that you can only initialize values in this simple way if you are dealing with objects and not numbers. Then you have to use Array.SetValue explicitly.

d = Double[4]

d[0] = 1.0

 

Will result in a: System.InvalidCastException: Unable to cast object of type

'System.Double[]' to type 'System.Object[]'.

 

You will need to do:

 

d:SetValue(0,1.0)

There are no implicit conversions of Lua tables into .NET types, but it is easy to do manually. Here is a useful function for creating an array of doubles from a table:

function make_double_array (tbl)

    local arr = Double[#tbl]

    for i,v in ipairs(tbl) do

        arr:SetValue(v,i-1)

    end

    return arr

end

Other collection types are treated similarly; generally, if the object is indexable, Lua will be able to index it naturally as well.

There is no direct support in Lua for enumerables, as there is in C# with the foreach statement, but it is not difficult to write a function that will allow us to iterate through any such collection using a Lua for statement:

function enum(o)

   local e = o:GetEnumerator()

   return function()

      if e:MoveNext() then

        return e.Current

     end

   end

end

 

for v in enum(args) do print(v) end