src/Type/Schema.php
public function isPossibleType(AbstractType $abstractType, ObjectType $possibleType)
    {
        if ($abstractType instanceof InterfaceType) {
            return $possibleType->implementsInterface($abstractType);
        }

        /** @var UnionType $abstractType */
        return $abstractType->isPossibleType($possibleType);
    }
public function isPossibleType(AbstractType $abstractType, ObjectType $possibleType)
    {
        if ($abstractType instanceof InterfaceType) {
            return $possibleType->implementsInterface($abstractType);
        }

        /** @var UnionType $abstractType */
        return $abstractType->isPossibleType($possibleType);
    }
Returns true if object type is concrete type of given abstract type
(implementation for interfaces and members of union type for unions)

@return bool

@api