[RFC] Pass $objectValue by reference when calling resolveType

[ruudk]

This allows the Interface or Union type resolver to modify the object value.

This is useful when you have a single entity that needs different representations. For example, when your data layer returns a generic PetEntity with a type discriminator, but your GraphQL schema has separate Dog and Cat types.

Example:

$PetType = new InterfaceType([
    'name' => 'Pet',
    'resolveType' => static function (PetEntity &$objectValue): string {
        if ($objectValue->type === 'dog') {
            $objectValue = new Dog($objectValue->name, $objectValue->woofs);
            return 'Dog';
        }

        $objectValue = new Cat($objectValue->name, $objectValue->meows);
        return 'Cat';
    },
    'fields' => ['name' => ['type' => Type::string()]],
]);

Now field resolvers receive the properly typed Dog or Cat object instead of the generic PetEntity,
allowing for type-safe resolution without needing to transform objects before they reach the type
resolver.

Common use cases:

• Database polymorphism (single table with type column)
• External APIs returning generic objects with type discriminators

Important

Unfortunately, this breaks the InterfaceType and UnionType contract. So this can only be done in a new major
But this serves as a RFC. Maybe there is a better non-breaking way to do this.

/cc @spawnia @simPod

[ruudk]

I think this is a better solution to the problem:

• Introduce resolveValue method to Interface and Union types #1776