Colon notation in object-oriented programming

[Dirk Laurie <dirk.laurie@...>]

2017-03-04 8:32 GMT+02:00 Petri Häkkinen <petrih3@gmail.com>:
> Why all the trouble? I mean, you could just use free functions:
> object_system_func(a, b, c)
>
> This is faster (no need for nested dynamic table look ups) and
> there is no need for "self" parameter that is magically more
> important than the others.

I and others replied to the above in the thread "Lua and composition",
but maybe it deserves a thread of its own.

Let me take an example from the only userdata objects supplied with
Lua, namely files.

One can write:

io.open("results.txt","w"):write(table.concat(results,"\n")):close()

Without colon notation, how far can we get?

local outfile = io.open("results.txt","w")

Now what next? Remember, outfile:write() is not available.
And io.write does not allow you to specify a file.

local filemeta = getmetatable(outfile).__index
filemeta.write(outfile,table.concat(results,"\n"))
filemeta.close(outfile)

Faster? Really? Clearer? Not on your nelly.

Now you can argue that the programmer is under no obligation
to hide the methods of a file object that well, but the point is that
you can't easily, by accident, call the write or close methods without
a valid file argument in place. This makes code safer and cleaner.