Curing the Common Loop

Trying to understand a complex function full of nested loops and conditionals is like trying to read a "choose your own adventure" book from front to back.

In this whirlwind tour of programming with collection pipelines, you'll learn how to use functional programming ideas to break down complex code and abstract hidden duplication behind expressive higher order functions.

Together we'll refactor ugly, complicated spaghetti into a series of simple, elegant transformations; free of loops, complex conditionals, and temporary variables.

Transcript

1. Curing the
   Common Loop
   @adamwathan
   

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2. $totalRevenue = 0;
   $minSales = 75000;
   foreach ($employees as $employee) {
   $employeeType = $employee->getType();
   if ($employeeType == 'Sales') {
   $customers = $employee->getCustomers();
   foreach ($customers as $customer) {
   $customerTotalSales = 0;
   foreach ($customer->getOrders() as $order) {
   $customerTotalSales += $order->total;
   }
   if ($customerTotalSales >= $minSales) {
   $totalRevenue += $customerTotalSales;
   }
   }
   }
   }
   return $totalRevenue;
   

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3. Higher Order
   FUNCTIONS
   

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4. Route::get('/', function () {
   return view('welcome');
   });
   

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5. Mail::send('order-shipped', $data, function ($m) {
   $m->to($this->customer->email);
   $m->subject("Your order has shipped!");
   });
   

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6. DB::transaction(function () use ($user) {
   $user->subscription()->delete();
   $user->update([
   'cancelled_at' => Carbon::now()
   ]);
   });
   

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7. Afford more powerful
   ABSTRACTIONS
   

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8. For example…
   

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9. $customerEmails = [];
   foreach ($customers as $customer) {
   $customerEmails[] = $customer->email;
   }
   return $customerEmails;
   

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10. $stockTotals = [];
    foreach ($inventoryItems as $item) {
    $stockTotals[] = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    }
    return $stockTotals;
    

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11. $customerEmails = [];
    foreach ($customers as $customer) {
    $customerEmails[] = $customer->email;
    }
    return $customerEmails;
    

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12. $customerEmails = [];
    foreach ($customers as $customer) {
    $email = $customer->email;
    $customerEmails[] = $email;
    }
    return $customerEmails;
    

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13. $stockTotals = [];
    foreach ($inventoryItems as $item) {
    $stockTotals[] = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    }
    return $stockTotals;
    

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14. $stockTotals = [];
    foreach ($inventoryItems as $item) {
    $stockTotal = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    $stockTotals[] = $stockTotal;
    }
    return $stockTotals;
    

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15. $stockTotals = [];
    foreach ($inventoryItems as $item) {
    $stockTotal = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    $stockTotals[] = $stockTotal;
    }
    return $stockTotals;
    

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16. $results = [];
    foreach ($items as $item) {
    $result = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    $results[] = $result;
    }
    return $results;
    

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17. $results = [];
    foreach ($items as $item) {
    $result = $item->email;
    $results[] = $result;
    }
    return $results;
    

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18. $results = [];
    foreach ($items as $item) {
    $result = $item->email;
    $results[] = $result;
    }
    return $results;
    

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19. $callback = function ($item) {
    return $item->email;
    };
    $results = [];
    foreach ($items as $item) {
    $result = $callback($item);
    $results[] = $result;
    }
    return $results;
    

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20. $results = [];
    foreach ($items as $item) {
    $result = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    $results[] = $result;
    }
    return $results;
    

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21. $callback = function ($item) {
    return [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    };
    $results = [];
    foreach ($items as $item) {
    $result = $callback($item);
    $results[] = $result;
    }
    return $results;
    

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22. $callback = function ($item) {
    return [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    };
    $results = [];
    foreach ($items as $item) {
    $result = $callback($item);
    $results[] = $result;
    }
    return $results;
    

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23. $callback = function ($item) {
    return $item->email;
    };
    $results = [];
    foreach ($items as $item) {
    $result = $callback($item);
    $results[] = $result;
    }
    return $results;
    

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24. function array_map($callback, $items) {
    }
    $results = [];
    foreach ($items as $item) {
    $result = $callback($item);
    $results[] = $result;
    }
    return $results;
    

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25. $customerEmails = [];
    foreach ($customers as $customer) {
    $customerEmails[] = $customer->email;
    }
    return $customerEmails;
    

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26. $customerEmails = array_map(function ($customer) {
    return $customer->email;
    }, $customers);
    

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27. $stockTotals = [];
    foreach ($inventoryItems as $item) {
    $stockTotals[] = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    }
    return $stockTotals;
    

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28. $stockTotals = [];
    foreach ($inventoryItems as $item) {
    $stockTotals[] = [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    }
    return $stockTotals;
    

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29. $stockTotals = array_map(function ($inventoryItem) {
    return [
    'product' => $item->productName,
    'total_value' => $item->quantity * $item->price,
    ];
    }, $inventoryItems);
    

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30. Another…
    

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31. $outOfStockProducts = [];
    foreach ($products as $product) {
    if ($product->isOutOfStock()) {
    $outOfStockProducts[] = $product;
    }
    }
    return $outOfStockProducts;
    

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32. $expensiveProducts = [];
    foreach ($products as $product) {
    if ($product->price > 100) {
    $expensiveProducts[] = $product;
    }
    }
    return $expensiveProducts;
    

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33. $results = [];
    foreach ($items as $item) {
    if ($item->price > 100) {
    $results[] = $item;
    }
    }
    return $results;
    

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34. $outOfStockProducts = [];
    foreach ($products as $product) {
    if ($product->isOutOfStock()) {
    $outOfStockProducts[] = $product;
    }
    }
    return $outOfStockProducts;
    

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35. $results = [];
    foreach ($items as $item) {
    if ($item->isOutOfStock()) {
    $results[] = $item;
    }
    }
    return $results;
    

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36. $results = [];
    foreach ($items as $item) {
    if ($item->isOutOfStock()) {
    $results[] = $item;
    }
    }
    return $results;
    

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37. $results = [];
    foreach ($items as $item) {
    if ($item->price > 100) {
    $results[] = $item;
    }
    }
    return $results;
    

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38. $callback = function ($item) {
    return $item->price > 100;
    };
    $results = [];
    foreach ($items as $item) {
    if ($callback($item)) {
    $results[] = $item;
    }
    }
    return $results;
    

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39. $results = [];
    foreach ($items as $item) {
    if ($item->isOutOfStock()) {
    $results[] = $item;
    }
    }
    return $results;
    

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40. $callback = function ($item) {
    return $item->isOutOfStock();
    };
    $results = [];
    foreach ($items as $item) {
    if ($callback($item)) {
    $results[] = $item;
    }
    }
    return $results;
    

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41. $callback = function ($item) {
    return $item->isOutOfStock();
    };
    $results = [];
    foreach ($items as $item) {
    if ($callback($item)) {
    $results[] = $item;
    }
    }
    return $results;
    

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42. $callback = function ($item) {
    return $item->price > 100;
    };
    $results = [];
    foreach ($items as $item) {
    if ($callback($item)) {
    $results[] = $item;
    }
    }
    return $results;
    

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43. function array_filter($items, $callback) {
    $results = [];
    foreach ($items as $item) {
    if ($callback($item)) {
    $results[] = $item;
    }
    }
    return $results;
    }
    $results = [];
    foreach ($items as $item) {
    if ($callback($item)) {
    $results[] = $item;
    }
    }
    return $results;
    

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44. $outOfStockProducts = [];
    foreach ($products as $product) {
    if ($product->isOutOfStock()) {
    $outOfStockProducts[] = $product;
    }
    }
    return $outOfStockProducts;
    

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45. $outOfStockProducts = array_filter($products, function ($product) {
    return $product->isOutOfStock();
    });
    

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46. $expensiveProducts = [];
    foreach ($products as $product) {
    if ($product->price > 100) {
    $expensiveProducts[] = $product;
    }
    }
    return $expensiveProducts;
    

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47. $expensiveProducts = array_filter($products, function ($product) {
    return $product->price > 100;
    });
    

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48. function getSalesEmails($employees) {
    $emails = [];
    foreach ($employees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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49. function getSalesEmails($employees) {
    $emails = [];
    foreach ($employees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    
    …map?
    

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50. function getSalesEmails($employees) {
    $emails = [];
    foreach ($employees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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51. Thinking in
    STEPS
    

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52. function getSalesEmails($employees) {
    $emails = [];
    foreach ($employees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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53. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($employees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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54. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($employees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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55. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($employees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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56. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($salesEmployees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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57. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($salesEmployees as $employee) {
    if ($employee->department === 'Sales') {
    $emails[] = $employee->email;
    }
    }
    return $emails;
    }
    

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58. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($salesEmployees as $employee) {
    $emails[] = $employee->email;
    }
    return $emails;
    }
    

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59. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($salesEmployees as $employee) {
    $emails[] = $employee->email;
    }
    return $emails;
    }
    

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60. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($salesEmployees as $employee) {
    $emails[] = $employee->email;
    }
    return $emails;
    }
    
    Map!
    

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61. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = [];
    foreach ($salesEmployees as $employee) {
    $emails[] = $employee->email;
    }
    return $emails;
    }
    

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62. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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63. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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64. Things I
    HATE
    

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65. #1. FOR LOOPS
    #2. CONDITIONALS
    #3. TEMP VARIABLES
    

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66. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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67. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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68. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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69. Inline
    TEMP
    

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70. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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71. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    return array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    }
    

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72. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    return array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    }
    

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73. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    return array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    }
    

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74. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    return array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    }
    

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75. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    return array_map(function ($employee) {
    return $employee->email;
    }, array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    }));
    }
    

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76. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    return array_map(function ($employee) {
    return $employee->email;
    }, array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    }));
    }
    

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77. function getSalesEmails($employees) {
    return array_map(function ($employee) {
    return $employee->email;
    }, array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    }));
    }
    

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78. The Problem With
    PRIMITIVES
    

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79. # => hello_there_laracon
    function toCamelCase($snakeString) {
    return lcfirst(
    str_replace(' ', '',
    ucwords(str_replace('_', ' ', $snakeString))
    )
    );
    }
    # => helloThereLaracon
    

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80. # => hello_there_laracon
    function toCamelCase($snakeString) {
    return $snakeString->replace('_', ' ')
    ->ucwords()
    ->replace(' ', '')
    ->lcfirst();
    }
    # => helloThereLaracon
    

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81. Introducing
    COLLECTIONS
    

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82. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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83. function getSalesEmails($employees) {
    $salesEmployees = array_filter($employees, function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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84. function getSalesEmails($employees) {
    $salesEmployees = $employees->filter(function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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85. function getSalesEmails($employees) {
    $salesEmployees = $employees->filter(function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = array_map(function ($employee) {
    return $employee->email;
    }, $salesEmployees);
    return $emails;
    }
    

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86. function getSalesEmails($employees) {
    $salesEmployees = $employees->filter(function ($employee) {
    return $employee->department == 'Sales';
    });
    $emails = $salesEmployees->map(function ($employee) {
    return $employee->email;
    });
    return $emails;
    }
    

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87. function getSalesEmails($employees) {
    return $employees->filter(function ($employee) {
    return $employee->department == 'Sales';
    })->map(function ($employee) {
    return $employee->email;
    });
    }
    

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88. Let’s write
    SOME CODE!
    

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89. http://www.fullstackradio.com
    FULL
    RADIO
    STACK
    

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90. @adamwathan
    adamwathan.me
    

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