On 25/08/2024 18:44, John Bafford wrote:
Although I'm not sold on the idea of using default as part of an
expression, I would argue that a default function parameter value is
fair game to be read and manipulated by callers. If the default value
was intended to be private, it shouldn't be in the function declaration.
There's an easy argument against this interpretation: child classes can
freely change the default value for a parameter, as long as they do not
make it mandatory. https://3v4l.org/SEsRm
That matches my intuition: that the public API, as a contract, states
that the parameter is optional; the specification of what happens when
it is not provided is an implementation detail.
For comparison, consider constructor property promotion; the caller
shouldn't know or care whether a class is defined as:
public function __construct(private int $bar) {}
or:
private int $my_bar;
public function __construct(int $bar) { $this->my_bar = $bar; }
The syntax sits in the function signature because it's convenient, not
because it's part of the API.
One important case where reading the default value could be important is
in interoperability with different library versions. For example, a
library might change a default parameter value between versions. If
you're using the library, and want to support both versions, you might
both not want to set the value, and yet also care what the default value
is from the standpoint of knowing what to expect out of the function.
This seems contradictory to me. If you use the default, you're telling
the library that you don't care about that parameter, and trust it to
provide a default.
If you want to know what the library did with its arguments, reflecting
the signature will never be enough anyway. For example, it's quite
common to write code like this:
function foo(?SomethingInterface $blah = null) {
if ( $blah === null ) {
$blah = self::_setup_default_blah();
}
// ...
}
A caller can't tell by looking at the signature that a new version of
the library has changed what _setup_default_blah() returns. If the
library doesn't provide an API to get $blah out later, then it's a
private detail that the caller has no business inspecting.
Regards,
--
Rowan Tommins
[IMSoP]
