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In the lua-5.2.0-alpha manual, at the beginning of section 6.5 - Table
Manipulation, it says:

"when we talk about the "length" of a table we mean the result of the
length operator"

In the definition for the length operator, it says:

"A program can modify the behavior of the length operator for any
value but strings through metamethods"

Therefore, I expect table.insert, table.remove, table.sort,
table.concat and table.unpack to honor the __len metamethod on tables,
since their description says that they work over the table length.

Yet, it doesn't work as documented:

> t = setmetatable({}, { __len = function(t) return 3 end })
> t[1], t[2], t[3], t[4], t[5] = "e", "d", "c", "b", "a"
> = #t

So far, so good; the length operator respects the length metamethod.

> =table.concat(t)

I expected only the first 3 strings to be concatenated (edc)

> table.sort(t)
> for i = 1, 5 do io.write(t[i]) end

I expected only the first 3 elements to be sorted (cdeba).

> print(table.unpack(t))
e	d	c	b	a

I expected to see only the first 3 strings:
e	d	c

Table.insert and table.remove don't respect the __len metamethod either.

In ltablib.c, I noticed that these functions called lua_rawlen instead
of lua_len. After changing them, I got the behaviour I expected.

I'm not sure if the bug is in the manual or in ltablib.c, but the
language seems more self-consistent when the functions in the table
module respect the __len metamethod.

- Keith