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- Subject: Re: Style question for user-defined types in C
- From: Sean Conner <sean@...>
- Date: Tue, 15 Feb 2011 04:14:52 -0500
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
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 -- 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