Bad Idea: Complex type hints for PHP7

Use the typical_set_type(string $alias, string $type) and typical_set_callback(string $alias, Callable $callback[, int $flags = 0]) functions to create psuedo typehints for use in running PHP7 scripts. These $alias types may then be used as Type Hints to function/method declarations.

Example uses

typical_set_type('NullableInt', '?int');

/* These two functions have effectively the same signature */
function foo(NullableInt $x) {}
function bar(?int $x) {}

Types can be combined using |(OR), &(AND), or ^(XOR) combinations:

typical_set_type('Scalar', 'bool | int | float');
typical_set_type('IndexableAndIterable', 'ArrayAccess & Iterable');
typical_set_type('IteratorOrExceptionButNotBoth', 'Iterable ^ Exception');

Or for even more complex types, use a callback:

typical_set_callback('Numberish', function ($arg, bool $strict) {
  if (is_int($arg) || is_float($arg)) {
    return $arg;
  }
  if (!$strict) {
    // Applies when called with strict_types=0 only
    if (is_null($arg) || is_bool($arg)) return intval($arg);

    if (is_object($arg)) $arg = strval($arg);
    if (is_numeric($arg)) return $arg;
  }
  throw new TypeError("Numberish type requires something numeric-like");
});

function double(Numberish $x) {
  return 2 * $x;
}
double(123); // OK
double(234.56); // OK
double("345.67"); // OK
double(new class() { function __toString() { return "5"; }}); // OK
double(new class() { function __toString() { return "hippo"; }}); // Error
double("banana"); // Error

Known Limitations

This extension makes the runtime do things it does't want to do, occaisionally the runtime fights back.

Initial values

Because the compiler sees aliases as class types, it complains about providing any default other than null. Thus the following will fail to compile:

typical_set_type('Foo', 'int');

function bar(Foo $x = 42) {}

Future Scope

Things I may add with time.

Negative Types

Prohibit accepting certain types, mostly useful with union/intersect types.

Generics

It should be trivially possible to provide support for expressions such as:

typical_set_type('IntArray', 'array<int>');
typical_set_type('Stream', 'resource<stream>');