Larry Garfield wrote on 20/04/2016 16:12:
On 4/20/16 10:01 AM, Rowan Collins wrote:
guilhermebla...@gmail.com wrote on 20/04/2016 03:54:
1- Even though mentioned, I'd still use "extends" or "implements"
instead
of "is" (which would be a new pseudo-reserved keyword) to enforce
data type
consistency and prevent developers to potentially referring to one
thing
while consider another.
Perhaps "instanceof" would make more sense here? "class
FileProcessor<T extends FileHandle>" seems to exclude instantiating
FileProcessor<FileHandle>, because "FileHandle extends FileHandle"
doesn't make any sense.
You could read "class Box<T instanceof Boxable>" as an assertion that
the class passes the constraint, as in "public function __construct(T
$t) { assert($t instanceof Boxable); }"
Regards,
I'm not an expert in generics by any means, but how is that different
than just
public function __construct(Boxable $t) {}
I thought the point of generics was for cases like "these two
variables must be the same type, but they can be any same type."
The is/extends/instanceof clause adds to the rule: "...they can be any
same type, *as long as that type meets this constraint*"
So using an unbounded generic, you could manually check:
class FileProcessor<T>
{
public function __construct(T $t) {
assert($t instanceof FileHandle);
}
}
$f = new FileProcessor<ZipArchiveEntryHandle>($zip->getEntryHandle(1));
// "T" is substituted for "ZipArchiveEntryHandle"
$f = new FileProcessor<int>(42); // assertion fails!
A bounded generic, using "is" as the keyword as in the current RFC,
performs the assertion for you:
class FileProcessor<T is FileHandle>
{
public function __construct(T $t) {
// no need for an assertion
}
}
$f = new FileProcessor<int>(42); // throws a TypeError
My suggestion was that the constraint is like an "instanceof" assertion,
so we could use that keyword:
class FileProcessor<T instanceof FileHandle>
{
public function __construct(T $t) {
// no need for an assertion
}
}
$f = new FileProcessor<int>(42); // throws a TypeError
I hope that makes sense.
Regards,
--
Rowan Collins
[IMSoP]
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