Introducing object attributes
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: Introducing object attributes
- From: Roland Illig <roland.illig@...>
- Date: 2004年11月05日 13:40:52 +0100
Hi,
after a really nice discussion on irc://irc.freenode.net/#Lua I'd like
to present my view on this topic in a more "conserving" medium than an
IRC session.
We discussed how to append things to an array and how to get the length
of an array.
My approach is a bit broader and comes from the Ada programming
language. I'd like to add some "attributes" to each value. These
attributes represent meta-data about the values, such as the type or a
table's size.
I chose the ASCII character #39 (single quote) for access to the
attributes of a type, because that's the way it looks like in Ada. The
choice for the single quote has been made because it looks like a
vertically mirrored dot. The dot represents access to the value's data,
while the single quote represents access to the meta-information, which
is kind of othogonal, hence the vertical mirroring.
Here is an example of how the code might look like.
table = {1, 2, 3, 4}
print table'lastindex
-- The number of elements stored in the array (read-only)
print table'size
-- The number of elements stored in the table (array + hash)
table'after = "first"
-- Append "first" to the table; table'after is a write-only lvalue
print table'type
-- print "table"
So far for the attributes of the tables. We should discuss which
attributes are suitable for each of the builtin Lua types.
all values:
type -- the type as returned by the type() function
image -- the value of the object as a string, appropriate
-- for being parsed by the Lua parser
-- (might be a problem for recursive tables and userdata)
nil, boolean, number, userdata:
-- no additional attributes
number:
maxvalue -- DBL_MAX for double, INT_MAX for int, ...
minvalue -- DBL_MIN for double, INT_MIN for int, ...
delta -- the minimum increase: 1 for int
string:
length -- see string.len()
function:
env -- see getfenv()
thread:
status -- see coroutine.status()
table:
lastindex -- A number n for which table[n] ~= nil and table[n] == nil
after -- A write-only lvalue that represents
-- table[table'lastindex + 1]
meta -- see getmetatable()
ipairs -- see ipairs()
pairs -- see pairs()
So far for now.
Roland