Re: Style question for user-defined types in C

[Sean Conner <sean@...>]

It was thus said that the Great Josh Haberman once stated:
> Suppose I have a user-defined type implemented in C.
> 
>   x = mytype.new()
> 
> Suppose my type has both data members (ie. passive) and methods
> which actually perform an action.  Is it preferred to use method
> calls for both?
> 
>   x:do_something(5)  -- Clearly should be a function.
>   x:name()  -- Called as a function, even though it's just data?
>   x.name    -- Returned as a string -- is this better?

  A project at work uses a custom read-only database file (could have
upwards of 100,000,000 small records; and they're pre-sorted as there's only
one key anyway).  I wrapped Lua around this database file using the
following:

	x = cdb.open(filename)	-- opens database file, returns user data
	
  x itself has a metatable associated with it, and thus you can do:

	entry = x:find(key)	-- find the entry associated with key
	x:close()		-- close the file, free resources, etc.

	#x			-- number of entries in data file
	entry = x[23]		-- reference 23rd entry in data file

  What's returned from x:find() or x[index] is a Lua table that corresponds
to the particular entry (a string and a bunch of flags).  Doing it this way
felt more natural than using a function to return an individual record. 
Looking back on this, I suppose I could have done:

	entry = x[key]

as well.  Hmm ... I could add that ... 

  Anyway, I did provide methods for __tostring, __gc, __index, __newindex
(to remind the other programers we can't change the data) and __len.  

> Aesthetically the last one seems more pleasing, since it makes clear
> that it's just returning some data.  But what do you all as Lua
> programmers expect?  I guess one downside of the second is that
> it might suggest that you can set it also, which is not allowed
> for my type:

  In my case, it's what felt better for the project, seeing how I'm
embedding Lua in a larger application (a testing suite for the project).  

> I want to make whatever choices are most idiomatic, but if there
> are any noticeable efficiency differences that is a factor too.

  I just went with what looked good to me.

  -spc (We're mostly a C/C++ shop, so idiomatic Lua isn't our top priority 8-P