Re: Allow default parameters before non-default ones?

On 13/12/2021 23:12, Kirill Nesmeyanov wrote:

I'll add that leading optional parameters are needed to implement currying and partial application.

function foo(int $opt = 42, int $req) {}

$foo = curry(foo(...), 23);

// $foo = fn($opt = 42, $req = 23);

I'm confused what the optional parameter is doing here - is it just to avoid telling the curry function which argument you're fixing? And wouldn't both currying and partial application result in a single-argument closure there, not just making both parameters optional? I would expect it to look something like this:

function foo(int $a, int $b) {}

$foo = partial(foo(...), 23, 0);

// $foo = fn($b) => foo(23, $b);

$foo = partial(foo(...), 23, 1);

// $foo = fn($a) => foo($a, 23);

$bar = curry(foo(...));

// $bar = fn($a) => fn($b) => foo($a, $b);

While this is not a popular practice in PHP, this deprecation notification «breaks» all code that uses functional pradigm/concepts.

That's clearly an exaggeration; it's clearly possible to write functional-style code without making use of this particular trick. If it is a *common* trick, then that's worth considering, but it would be good to see some evidence of that. Regards, -- Rowan Tommins [IMSoP]