Re: 5.1 collectgarbage: test case

["Adam D. Moss" <adam@...>]

Michael Broughton wrote:
> This is normal. Lua grows it memory pool as needed, it does not reduce 
> it. also, collectgarbage("count") reports the current size of Lua's 
> memory pool, not how much of the pool is being used.

Not... entirely... correct on either count!

t = {}
for n = 1,10000 do
    table.insert(t,n)
end
collectgarbage("collect")
print("MEM:",collectgarbage("count"))
for n = 1, #t-1 do
    table.remove(t, 1)
 end
t.foo= "bar" -- <---- LOOK!  MAGIC!
collectgarbage("collect")
print("MEM:",collectgarbage("count"))
table.foreach(t,print)

prints:
MEM:    210.0732421875
MEM:    18.1123046875
1       10000
foo     bar

The (well-discussed, but perhaps not documented, as an
implementation detail) reason is that Lua only considers
shrinking a table's allocation on a non-nil new-index
write.  (Empirically only a non-array non-nil new-index
write, at that.)

Cheers,
--Adam