[An ongoing series of "don't repeat yourself"
peeves.]
On Mar 23, 2014 9:50 AM, "Roberto Ierusalimschy" <roberto@inf.puc-rio.br>
wrote:
> The traditional method is this:
>
> local buffer = {} -- create a buffer
>
> buffer[#buffer + 1] = x -- add values
LambdaMOO[1] has sugar for this:
buffer[# + 1] = x
in which # is shorthand for length() of the innermost
subscripted _expression_. Since MOO lists are immutable and
length() cannot be overriden, the semantics can be fuzzy. For
Lua it would be something like
local tmp = buffer
tmp[#tmp + 1] = x
and in general calling apply('#', tmp) every place a
0-ary # is encountered. We already evaluated the object to be
indexed, so tmp is on the stack I think. Anyway
buffer[#] = nil
is the other idiom. More generally, this allows
addressing from the end of the array, filling the same niche
negative index values do in the stack API.
I note with some amusement that #-1 is stack -2 and
#-0 is stack -1.
Jay
[1]: It's actually buffer[$] in MOO. The syntax
"#1234" is a literal for an objnum, a reference to an object.
The system object, #0, has a bunch of special functions; one is
as a registry of public identifiers. "$foo" is sugar for
"#0.foo".
I have to say, I really like that. Much better to understand than
negative indices, and of course you are able to address elements
that are currently not (yet) in the list.
