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                <?php  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                /*  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                * This file is a part of graphql-youshido project.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                *  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                * @author Alexandr Viniychuk <[email protected]>  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                * created: 11/30/15 1:30 AM  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                namespace Youshido\GraphQL\Type\Config\Field;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Youshido\GraphQL\Type\Config\Config;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Youshido\GraphQL\Type\Object\AbstractObjectType;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Youshido\GraphQL\Type\TypeInterface;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Youshido\GraphQL\Type\TypeMap;  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                class FieldConfig extends Config  | 
            
            
                                                                        
                            
            
                                    
            
            
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                { | 
            
            
                                                                        
                            
            
                                    
            
            
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                    public function getRules()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return [  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'name'              => ['type' => TypeMap::TYPE_STRING, 'required' => true],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'type'              => ['type' => TypeMap::TYPE_ANY, 'required' => true],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'args'              => ['type' => TypeMap::TYPE_ARRAY],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'required'          => ['type' => TypeMap::TYPE_BOOLEAN],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'description'       => ['type' => TypeMap::TYPE_STRING],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'resolve'           => ['type' => TypeMap::TYPE_FUNCTION],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'deprecationReason' => ['type' => TypeMap::TYPE_STRING],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        ];  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                    }  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    public function resolve($value = null, $args = [])  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $resolveFunction = $this->get('resolve', null); | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        if($resolveFunction && is_callable($resolveFunction)) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                           return $resolveFunction($value, $args);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return $this->getType()->resolve($value, $args);  | 
            
                            
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                    }  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                        
                            
            
                                    
            
            
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                     * @return TypeInterface|AbstractObjectType  | 
            
            
                                                                        
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function getType()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return $this->data['type'];  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                    }  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    public function isRequired()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return $this->get('required', false); | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                    }  | 
            
            
                                                        
            
                                    
            
            
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                }  | 
            
            
                        
Let’s take a look at an example:
In the above example, the authenticate() method works fine as long as you just pass instances of MyUser. However, if you now also want to pass a different implementation of User which does not have a getDisplayName() method, the code will break.
Available Fixes
Change the type-hint for the parameter:
Add an additional type-check:
Add the method to the interface: