Function Overloading?

[Layback_]

Since functions in Lua does not have its parameter types defined from function declaration, this could be not an ideal to utilize the concept of 'Function Overloading'.

However, according to this page, you could still overload functions in Lua as well (but not a straight-forward approach like that is in C++ or Java).

I'm asking this because of :SetPoint(...) function.

On Wowwiki, it introduces four different ways to call :SetPoint(...) method which are:

obj:SetPoint(point, relativeFrame, relativePoint, ofsx, ofsy);
obj:SetPoint(point, relativeFrame, relativePoint);
obj:SetPoint(point, ofsx, ofsy);
obj:SetPoint(point);

As we all know, data type for 2nd and 3rd approach are totally different (apart from 'point' i mean).

So, my question is that does anyone here know whether this is done via fucntion overloading approach or via some other method like variable type checking?

e.g.

if type(arg2) == "number" then
    ...
elseif type(arg2) == "string" then
    ...
end

[Resike]

You can get the number of incoming arguments like this:

function Legion(...)
    local argnum = select("#", ...)
    if argnum  == 5 then
 
    elseif argnum == 4 then
 
    else
 
    end
end

[Layback_]

Originally Posted by Resike You can get the number of incoming arguments like this: function Legion(...)     local argnum = select("#", ...)     if argnum  == 5 then       elseif argnum == 4 then       else       end end

Hi Resike,

Yeah I'm aware of that

But is :SetPoint method also written that way?

[Resike]

Originally Posted by Layback_ Hi Resike, Yeah I'm aware of that But is :SetPoint method also written that way?

I'm not sure, but i wouldn't be surprised. And unless you want to do something really funky thats the easiest method.

[lightspark]

Originally Posted by Layback_ Hi Resike, Yeah I'm aware of that But is :SetPoint method also written that way?

No, cuz it's implemented in C++, probably, I'm mostly certain it's

[SDPhantom]

C API functions are written a lot different than Lua functions. A C function gets the Lua state as its only argument. C-side functions can be called on the state to see how many arguments were passed from the Lua engine and pop the values from the stack. The function is expected to push returns to the stack and return the number of values that were pushed.

This example is in the lua_CFunction section of the Lua 5.1 reference manual.

static int foo (lua_State *L) {
    int n = lua_gettop(L);  /* number of arguments */
    lua_Number sum = 0;
    int i;
    for (i = 1; i <= n; i++) {
        if (!lua_isnumber(L, i)) {
            lua_pushstring(L, "incorrect argument");
            lua_error(L);
        }
        sum += lua_tonumber(L, i);
    }
    lua_pushnumber(L, sum/n);   /* first result */
    lua_pushnumber(L, sum);     /* second result */
    return 2;                   /* number of results */
}

[Layback_]

Many thanks to Resike, lightspark and especially to SDPhantom

Did not really give an attention to reference manual page, but looks interesting!

I'll probably use the method that Resike suggested as I also think that would be the easiest way

[Phanx]

Originally Posted by Resike function Legion(...)     local argnum = select("#", ...)     if argnum  == 5 then       elseif argnum == 4 then       else       end end

Another way to do this would be to just assign all the parameters to variables (up to the max accepted) and then check if they exist. Here's an example of how you might handle the current functionality of SetPoint in pure Lua:

function Frame:SetPoint(point, relTo, relPoint, x, y)
    if y then
        -- "TOPLEFT", UIParent, "CENTER", 5, 20
    elseif x then
        -- "TOPLEFT", UIParent, 5, 20
        relPoint, x, y = point, relPoint, x
    elseif relPoint then
        if type(relTo) == "number" then
            -- "TOPLEFT", 5, 20
            relTo, relPoint, x, y = self:GetParent(), point, relTo, relPoint
        else
            -- "TOPLEFT", UIParent, "CENTER"
            x, y = 0, 0
        end
    elseif relTo then
        -- "TOPLEFT", UIParent
        relPoint, x, y = point, 0, 0
    elseif point then
        -- "TOPLEFT"
        relTo, relPoint, x, y = self:GetParent() point, 0, 0
    end
    -- Now you have all the expected arguments
    -- and can do whatever you want with them.
end

In practice you'd also want additional sanity checks for missing values in the middle of the list (not sure what the real SetPoint actually does if you pass something like "TOPLEFT", nil, "CENTER") and value types (x/y need to be numbers, so use tonumber and fall back to 0; relTo needs to be a frame reference, so look up strings in _G and fall back to the frame's parent if you can't resolve it to a frame; etc).