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Date: Fri, 14 May 2021 19:36:33 -0500
To: "php internals" <internals@lists.php.net>
Content-Type: text/plain
Subject: Re: [PHP-DEV] [RFC] Partial function application
From: larry@garfieldtech.com ("Larry Garfield")

On Fri, May 14, 2021, at 7:20 PM, Aaron Piotrowski wrote:
> 
> > On May 14, 2021, at 7:00 PM, Larry Garfield <larry@garfieldtech.com> wrote:
> > 
> > Is that actually going to come up?  Given that PHP functions (at least user-space ones) accept extra trailing arguments and just let them fall off, I would *expect* a closure that way to do the same.  Named arguments continue that, I believe, by just ignoring any variadic arguments that do not match a parameter in the function.  It seems odd to go back on that behavior now.
> 
> I don't consider forwarding extra arguments an issue. I briefly was 
> thinking it might be nice to be explicit about the number of arguments 
> a partial would accept, but you convinced me otherwise in R11, so I 
> think we're on the same page here.
> 
> > 
> > I can't speak for the others, but I could tolerate making "more than one extra ? beyond the end of the parameter list is an error", potentially, as at that point they're redundant.  But if a function has, say, 4 params, then fourParams(1, 3, ?) is a convenient way to say "and placeholder everything else".  Especially in dynamic cases like Nicolas pointed out, you may not necessarily know how many arguments there are.
> 
> With what I proposed in my last email, `fourParams(1, 3, ?)` is 
> acceptable, there's nothing superfluous there. At least one ? is needed 
> to declare a partial. Similarly, a partial for a no parameter function: 
> `$partial = functionTakingNoParams(?)`. Or even a partial with args 
> bound to all four params: `fourParams(1, 2, 3, 4, ?)`.
> 
> What would error is `fourParams(1, 3, ?, ?)`, as the second ? is meaningless.
> 
> I think you've convinced me that one-for-one matching on ? is 
> burdensome, but the above is a happy medium perhaps?

I'd be OK with "no more than one trailing ? in excess of what the underlying callable has."  (Which means if you don't know, just stick one ? at the end and you know it will work.)

--Larry Garfield