ReflectionProperty クラス

I think a more accurate explanation is this:The Reflection classes are designed to reflect upon the source code of an application, not on any runtime information.I think you misunderstand the ReflectionProperty constructor in your example above. The fact that it accepts an object as argument is just a convenience feature - you are actually inspecting the class of that object, not the object itself, so it's basically equivalent to:<?php// works fine $Reflection = new ReflectionProperty(get_class($a), 'a');// throws exception $Reflection = new ReflectionProperty(get_class($a), 'foo');?>Getting the class of the object you're passing in is implied, since inspecting a defined property is the purpose of this class.In your example, $a->foo is a dynamic member - it is not defined as a member of class, so there is no defining class reference, line number, default value, etc. - which means, there is nothing to reflect upon.Clearly this very useful library could use some real documentation...

There is way to get property type without reflection.Not very clear, but there is:<?phpfunction getPropType(object $object, string $propName): string{    try {        $object->{$propName} = new class {};    } catch (\TypeError $e) {        // @hint: question mark in type can be used to detect if property is nullable        if (preg_match('/of type \??(.*)$/', $e->getMessage(), $m)) {            return $m[1];        }        throw $e;    } catch (\Error $e) {        // property doesn't exist or is not public        throw $e;    }    throw new \TypeError(sprintf('Property %s of class %s has no type', $propName, $object::class));    // alternatively return 'mixed';}?>note: in case you need access to private/protected properties its easy to change this to be embedded in any class:<?phptrait PropertyTypeResolver{    public function getPropType(string $propName): string    {        try {            $this->{$propName} = new class {};        } catch (\TypeError $e) {            // @hint: question mark in type can be used to detect if property is nullable            if (preg_match('/of type \??(.*)$/', $e->getMessage(), $m)) {                return $m[1];            }            throw $e;        } catch (\Error $e) {            // property doesn't exist            throw $e;        }        throw new \TypeError(sprintf('Property %s of class %s has no type', $propName, $this::class));        // alternatively return 'mixed';    }}?>