> Besides, it would be useful to have non-constant to-be-closed variables
So, what exactly should happen in this code?
local <toclose> f = io.open("a")
local x = f
f = io.open("b") -- should 'a' be closed? or not because of x
f = io.open("c") -- should 'b' be closed?
In your example only the last value in variable f would be evicted.
Simple example how non-constant to-be-closed variable might be useful:
when you need to reopen a file during file operations (close the file, open it again with another access mode, save new file value into the to-be-closed variable)
It is not known in compile-time would you need to re-open file or not.
This situation requires to-be-closed variable to be writable.
do
local <toclose> f = io.open("a")
...
if need_to_reopen_this_file then
f:close()
f = io.open(...)
end
...
end -- evict the file value from f
Another possible situation - you are reading multi-volume archive.
Only one volume file is opened at any given time.
To switch a volume, you close the current volume file and open the next volume file.
Single to-be-closed variable is enough to guarantee that the last opened volume file will be closed on eviction.
