Re: Trailing nils in an argument list
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- Subject: Re: Trailing nils in an argument list
- From: David Kastrup <dak@...>
- Date: 2011年1月09日 16:57:13 +0100
Dirk Laurie <dpl@sun.ac.za> writes:
> On Sun, Jan 09, 2011 at 04:51:00PM +0200, David Kastrup wrote:
>> Dirk Laurie <dpl@sun.ac.za> writes:
>>
>> > 6. insert(a,b) does not do the same as insert(a,b,nil). This
>> > behaviour would not be possible for a function of three arguments
>> > written in Lua itself.
>>
>> Huh?
>>
>> function arity(...)
>> return select('#',...)
>> end
>> print(arity(1,2),arity(1,2,nil))
>>
>> returns
>>
>> 2 3
>>
> By 'a function of three arguments' I mean a function starting with e.g.
>
> function f(a,b,c)
A "function of three arguments" receives three arguments by demand and
coercion. It is somewhat silly to complain that it can't distinguish
getting a different number.
I don't see that a function starting with e.g.
function f(a,b,...)
can't be used as a function of two _or_ three arguments perfectly well.
You could try arguing that f in this case does not raise an error when
called with 4 arguments. But neither does insert, or any Lua function.
Spurious arguments are always allowed and ignored.
--
David Kastrup