Actually executing Hack code doesn't necessarily typecheck everything. You need to actually run a separate tool to enforce the type system, as described in the docs article linked here. When you do that, you'll get an error that looks something like this, depending on the exact version of HHVM you have:
File "shapes.php", line 10, characters 19-23:
Invalid argument (Typing[4110])
File "shapes.php", line 3, characters 41-43:
This is an int
File "shapes.php", line 10, characters 42-76:
It is incompatible with a string
Modern versions of HHVM will also yell at you if you aren't running the typechecker; I suspect you're running an older version, before we realized this was a point of confusion -- sorry!
What actually happens when you run type-incorrect code is undefined behavior. The answer by Ed Cottrell is correct for the current version of HHVM -- we do the same thing PHP does to coerce types -- but keep in mind it's undefined behavior and may change in future versions without notice.
Answer from Josh Watzman on Stack Overflow'Hack' or library or tool that lets you create shapes that you can copy on the rM2
hacklang - How to access optional shape field in hack? - Stack Overflow
Feature UI hack help
How to instantiate a shape type object in hacklang - Stack Overflow
Videos
Actually executing Hack code doesn't necessarily typecheck everything. You need to actually run a separate tool to enforce the type system, as described in the docs article linked here. When you do that, you'll get an error that looks something like this, depending on the exact version of HHVM you have:
File "shapes.php", line 10, characters 19-23:
Invalid argument (Typing[4110])
File "shapes.php", line 3, characters 41-43:
This is an int
File "shapes.php", line 10, characters 42-76:
It is incompatible with a string
Modern versions of HHVM will also yell at you if you aren't running the typechecker; I suspect you're running an older version, before we realized this was a point of confusion -- sorry!
What actually happens when you run type-incorrect code is undefined behavior. The answer by Ed Cottrell is correct for the current version of HHVM -- we do the same thing PHP does to coerce types -- but keep in mind it's undefined behavior and may change in future versions without notice.
The interpreter will try to evaluate the 'y' key as a number to do the calculation.
Example:
echo 4 * '6';
// prints 24
echo 4 * '6foo';
// prints 24
echo 'foo' * 42;
// prints 0, because floatval('foo') === 0
Your situation is like the third example. floatval('this should cause an fatal error?') === 0, so the calculation is:
b['x'] + 
b['y'] === 3 * 4 + 0 * 4 === 12
I distinctly recall seeing something like that but couldn't find it again when I searched: I want to make things like check boxes, check marks and other little symbols that I can copy and paste in my documents. If you manually make a PNG or PDF, those things are not copyable, but there was a tool that would let you make documents with shapes that you could copy, just as if you'd written/drawn them yourself. Anyone got a name or link for me ?
Ok, found it: https://docs.hhvm.com/hack/reference/class/HH.Shapes/idx/
So the correct way is,
Shapes::idx($rcvd, 'bar');
You can use the Shapes::idx method as you mentioned in your answer.
but you can also use null coalesce operator, which you might be more familiar with from other programming languages such as PHP and C#.
see : https://docs.hhvm.com/hack/expressions-and-operators/coalesce
example :
type Foo = shape(
'bar' => ?int,
?'baz' => int,
);
function qux(Foo $foo): int {
$default = 1;
// foo[bar] is null ? set default.
$bar = $foo['bar'] ?? $default;
// foo[baz] doesn't exist ? set default.
$baz = $foo['baz'] ?? $default;
return $baz + $bar;
}
<<__EntryPoint>>
async function main(): Awaitable<noreturn> {
echo qux(shape(
'bar' => null,
)); // 2
echo qux(shape(
'bar' => 0,
)); // 1
echo qux(shape(
'bar' => 1,
)); // 2
echo qux(shape(
'bar' => 4,
'baz' => 2,
)); // 6
echo qux(shape(
'bar' => null,
'baz' => 0
)); // 1
}
Hack also support null coalesce equal operator.
example :
// foo[bar] is null ? set foo[bar] to default
$foo['bar'] ??= $default;
// foo[baz] is missing ? set foo[baz] to default
$foo['baz'] ??= $default;