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                <?php  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                namespace Iris\Mapping;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                class SimpleCollection extends Base  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * {@inheritdoc} | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function assign(array $externalData)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $simpleCollection = new \Iris\Transfer\Catalog\SimpleCollection;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        foreach ($externalData as $c) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $simpleCollection[] = new \Iris\Transfer\Catalog\Simple([  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'sku'              => $c['sku'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'variation'        => $c['variation'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'brand'            => $c['brand'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'color'            => $c['color'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'gender'           => $c['gender'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'color_family'     => $c['color_family'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'box_height'       => $c['box_height'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'box_width'        => $c['box_width'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'box_length'       => $c['box_length'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'weight'           => $c['weight'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'color_name_brand' => $c['color_name_brand'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'quantity'         => $c['quantity'],  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                'barcode_ean'      => $c['barcode_ean']  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            ]);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return $simpleCollection;  | 
            
                            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * {@inheritdoc} | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @param \Iris\Transfer\Catalog\SimpleCollection $internalData  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                     */  | 
            
            
                                                        
            
                                    
            
            
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                    public function map($internalData)  | 
            
            
                                                        
            
                                    
            
            
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                    { | 
            
            
                                                        
            
                                    
            
            
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                        $externalData = [];  | 
            
            
                                                        
            
                                    
            
            
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                        foreach ($internalData as $simple) { | 
            
            
                                                        
            
                                    
            
            
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                            $externalData[] = [  | 
            
            
                                                        
            
                                    
            
            
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                                'sku'              => $simple->getSku(),  | 
            
            
                                                        
            
                                    
            
            
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                                'variation'        => $simple->getVariation(),  | 
            
            
                                                        
            
                                    
            
            
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                                'brand'            => $simple->getBrand(),  | 
            
            
                                                        
            
                                    
            
            
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                                'color'            => $simple->getColor(),  | 
            
            
                                                        
            
                                    
            
            
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                                'gender'           => $simple->getGender(),  | 
            
            
                                                        
            
                                    
            
            
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                                'color_family'     => $simple->getColorFamily(),  | 
            
            
                                                        
            
                                    
            
            
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                                'box_height'       => $simple->getBoxHeight(),  | 
            
            
                                                        
            
                                    
            
            
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                                'box_width'        => $simple->getBoxWidth(),  | 
            
            
                                                        
            
                                    
            
            
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                                'box_length'       => $simple->getBoxlength(),  | 
            
            
                                                        
            
                                    
            
            
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                                'weight'           => $simple->getWeight(),  | 
            
            
                                                        
            
                                    
            
            
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                                'color_name_brand' => $simple->getColorNameBrand(),  | 
            
            
                                                        
            
                                    
            
            
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                                'quantity'         => $simple->getQuantity(),  | 
            
            
                                                        
            
                                    
            
            
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                                'barcode_ean'      => $simple->getBarcodeEan()  | 
            
            
                                                        
            
                                    
            
            
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                            ];  | 
            
            
                                                        
            
                                    
            
            
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                        }  | 
            
            
                                                        
            
                                    
            
            
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                        return $externalData;  | 
            
            
                                                        
            
                                    
            
            
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                    }  | 
            
            
                                                        
            
                                    
            
            
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                }  | 
            
            
                                                        
            
                                    
            
            
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If you return a value from a function or method, it should be a sub-type of the type that is given by the parent type f.e. an interface, or abstract method. This is more formally defined by the Lizkov substitution principle, and guarantees that classes that depend on the parent type can use any instance of a child type interchangably. This principle also belongs to the SOLID principles for object oriented design.
Let’s take a look at an example:
Our function
my_functionexpects aPostobject, and outputs the author of the post. The base classPostreturns a simple string and outputting a simple string will work just fine. However, the child classBlogPostwhich is a sub-type ofPostinstead decided to return anobject, and is therefore violating the SOLID principles. If aBlogPostwere passed tomy_function, PHP would not complain, but ultimately fail when executing thestrtouppercall in its body.