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Date: Sun, 15 Oct 2023 14:04:53 +0200
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Subject: Re: [PHP-DEV] DOMXPath / XSLTProcessor function callbacks
From: dossche.niels@gmail.com (Niels Dossche)

Hi Marc

On 10/15/23 12:53, Marc wrote:
> Hi,
> 
> On 14.10.23 13:54, Niels Dossche wrote:
>> Hi Tim
>>
>> On 10/14/23 12:30, Tim Düsterhus wrote:
>>> Hi
>>>
>>> On 10/13/23 00:39, Niels Dossche wrote:
>>>> Please let me know your thoughts.
>>> What does calling ->registerPHPFunctions() do when it's called more than once? Will the existing allow-list be overwritten or amended?
>>>
>>> i.e.
>>>
>>> $xpath->registerPHPFunctions([
>>>    'strtoupper',
>>> ]);
>>> $xpath->registerPHPFunctions([
>>>    'ucfirst',
>>> ]);
>>>
>>> will I be able to:
>>>
>>> (a) Call ucfirst(), but not strtoupper()
>>> (b) Call both
>> You can call both, it's additive.
> 
> As it's not clear what these functions do wouldn't it make more sense to introduce new / more clear functions and deprecate the old?
> 
> Like:
> 
> ->addXPathCallable(string $alias, callable $fn);
> ->getXPathCallables(): array<string, callable>
> ->removeXPathCallable(string $alias);

This would be the cleaner option.
The question here is how they would interact with each other and the existing registerPhpFunctions():
- addXPathCallable() when the alias already exists: I guess throw a ValueError
- remove and get should likely also act on the functions registered via registerPhpFunctions()
- What should happen when we call registerPhpFunctions() followed by addXPathCallable("foo", function ($...) {...});
  Probably both global functions and foo should be callable. But what should happen then when there is also a global function foo, which one should be called? Probably the explicitly registered callable?

What's currently also weird is that in the following snippet:
```
$xpath->registerPhpFunctions();
$xpath->registerPhpFunctions("ucfirst");
```
then only ucfirst() would be callable, which is surprising especially considering that calling $xpath->registerPhpFunctions("otherfunction") afterwards will make both ucfirst and otherfunction callable.

> 
> And is it really necessary to be able to register all functions? Also what would happen in this case with functions included later? Would they also be callable or only the functions known at the point of registering?
> 

For the first question: unlikely.
For the second question: they would also be callable.

>>> Best regards
>>> Tim Düsterhus
>> Cheers
>> Niels
> 
> 
> Best,
> Marc
> 

Cheers
Niels