Re: Confusive text in Lua doc "Variable Number of Arguments" about "arg"

[Xmilia Hermit <xmilia.hermit@...>]

Philippe Verdy wrote:

Note that that page of documentation uses an usual non-sense notation to describe the content of the local parameter named "arg" (implicitly declared in all functions):

arg={5, 8; n=2}

This notation uses a semicolon in a table constructor, a syntax that does not exist in Lua.

    It does exist in lua. In tables one can use either ',' or ';' as
    separator as stated in the manual:
    https://www.lua.org/manual/5.2/manual.html#9,
    https://www.lua.org/manual/5.0/manual.html#BNF.

It may suggest that this semicolon indicates that the key/value pair n=2 is not stored in the table itself, but in its metatable.

    It was used in earlier versions of lua to separate array and
    key-value parts. (see
    https://www.lua.org/manual/4.0/manual.html#BNF)

Such observation cannot be made, but if it does, then any declared function that explicitly accesses to its "arg" parameter could have to create (on function entry) a new table indexing all upvalues (including nil values), and another table to store the key/value pair with an implicit key name 'n' (here ['n'] = 2) containing the effective number of upvalues (including nil's).

Such creation of two tables would be very inefficient (stressing the garbage collector), so I suspect that instead the "arg" type is not a true "table" but behaves "like a table" in user's Lua code.

    Look at the sources. Here
https://github.com/lua/lua/blob/98194db4295726069137d13b8d24fca8cbf892b6/ldo.c#L220
    a normal table is created for the args table without a metatable.
    There is no special type for the args table nor has it only an array
    part.
    
    I do not comment on the further points since they build upon these
    wrong asumptions.
    
    Regards,
    Xmilia