Rethinking Loops

John Kary • @johnkary

FizzBuzz

Print numbers from 1 to 100, but...
For multiples of 3 print "Fizz"
For multiples of 5 print "Buzz"
For multiples of both 3 and 5 print "FizzBuzz"


$ php fizzbuzz.php
1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz
16
...
Buzz


foreach (range(1,100) as $num) {
    $output = '';

    if (0 === $num % 3) {
        $output .= 'Fizz';
    }

    if (0 === $num % 5) {
        $output .= 'Buzz';
    }

    if (!$output) {
        $output = $num;
    }

    echo $output . "\n";
}


$max = 100;
$all = range(1, $max);
$threes = array_fill_keys(range(3, $max, 3), 'Fizz'); // [3 => 'Fizz', 6 => 'Fizz']
$fives = array_fill_keys(range(5, $max, 5), 'Buzz');  // [5 => 'Buzz', 10 => 'Buzz']
$fifteens = array_fill_keys(range(15, $max, 15), 'FizzBuzz'); // [15 => 'FizzBuzz']

echo join("\n", array_replace($all, $threes, $fives, $fifteens));

By Jeff Madsen @codebyjeff

What if we used arrays for (almost) everything?

Functional Programming


(defn encode
  [#^InputStream input #^Writer output #^String alphabet line-length]
  (let [buffer (make-array Byte/TYPE 3)]
    (loop [line 0]
      (let [len (.read input buffer)]
        (when (pos? len)
          (let [b0 (Integer/valueOf (int (aget buffer 0)))
                b1 (Integer/valueOf (int (aget buffer 1)))
                b2 (Integer/valueOf (int (aget buffer 2)))]
            (cond (= len 3)
                  (let [s0 (bit-and 0x3F (bit-shift-right b0 2))
                        s1 (bit-and 0x3F
                                    (bit-or (bit-shift-left b0 4)
                                            (bit-shift-right b1 4)))
                        s2 (bit-and 0x3F
                                    (bit-or (bit-shift-left b1 2)
                                            (bit-shift-right b2 6)))
                        s3 (bit-and 0x3F b2)]
                    (.append output (.charAt alphabet s0))
                    (.append output (.charAt alphabet s1))
                    (.append output (.charAt alphabet s2))
                    (.append output (.charAt alphabet s3))))))))))

array_map


// array_map ( callable $callback , array $array1 [, array $... ] )

$start = [1, 2, 3, 4, 5];
$end = array_map(function ($i) {
    return $i * 2;
}, $start);

// [2, 4, 6, 8, 10]

array_filter


// array_filter ( array $array [, callable $callback [, int $flag = 0 ]] )

$start = [1, 2, 3, 4, 5, 6];
$even = array_filter($start, function ($i) {
    return $i % 2 === 0;
});

// [2, 4, 6]

array_reduce


// array_reduce ( array $array , callable $callback [, mixed $initial = NULL ] )

$start = [1, 2, 3, 4, 5];
$end = array_reduce($start, function ($total, $i) {
    return $total + $i;
}, 0);

// 15

Expressive Language

Cool

Chess is cool
Roller coasters are cool
Playing chess on a roller coaster is cool

Cool

Chess is contemplative
Roller coasters are thrilling
Playing chess on a roller coaster is connivingly rebellious

Expressive Code

array_map


$start = [1, 2, 3, 4, 5];
$end = [];

for ($i=0; $i < count($start); $i++) {
    $current = $start[$i];
    $end[] = $current * 2;
}

// $end [2, 4, 6, 8, 10]


$start = [1, 2, 3, 4, 5];
$end = array_map(function ($i) {
    return $i * 2;
}, $start);

// $end [2, 4, 6, 8, 10]

array_filter


$start = [1, 2, 3, 4, 5, 6];
$even = [];

foreach ($start as $i) {
    if ($i % 2 === 0) {
        $even[] = $i;
    }
}

// $even [2, 4, 6]


$start = [1, 2, 3, 4, 5, 6];
$even = array_filter($start, function ($i) {
    return $i %2 === 0;
});

// $even [2, 4, 6]

array_reduce


$start = [1, 2, 3, 4, 5];
$end = 0;

foreach ($start as $s) {
    $end = $end + $s;
}

// $end === 15


$start = [1, 2, 3, 4, 5];
$end = array_reduce($start, function ($end, $i) {
    return $end + $i;
}, 0);

// $end === 15
// $end = array_sum($start);

Defining a global function


function sayHello($name) {
    return 'Hello ' . $name;
}

echo sayHello("John"); // "Hello John"

Defining a static function


class User {
    public static function sayHello($name) {
        return 'Hello ' . $name;
    }
}

echo User::sayHello("John"); // "Hello John"

Defining an object method


class User {
    private $name;

    public function __construct($name) {
        $this->name = $name;
    }

    public function sayHello() {
        return 'Hello ' . $this->name;
    }
}

$user = new User("John");
echo $user->sayHello();  // "Hello John"

Defining anonymous functions


$sayHello = function ($name) {
    return 'Hello ' . $name;
};

echo $sayHello('John'); // "Hello John"

Scope


$method = "GET";

sayHello('John');

function sayHello($name) {
    return 'Hello ' . $name . ' via ' . $method;
    // PHP Notice:  Undefined variable: method
}

Scope


$method = "GET";

sayHello('John');
// "Hello John via GET"

function sayHello($name) {
    global $method;
    return 'Hello ' . $name . ' via ' . $method;
}

Scope


$method = "GET";

function sayHello($name, $verb) {
    return sprintf('Hello %s via %s', $name, $verb);
}

echo sayHello('John', $method); // "Hello John via GET"

Scope


function sayHello($name) {
    return 'Hello ' . $name;
}

sayHello('John'); // "Hello John"
echo $name;
// `PHP Notice: Undefined variable: name ...`
// because $name is not accessible in enclosing scope

Scope


$method = "GET";

$greeting = function($name) use ($method) {
    return sprintf('Hello %s via %s', $name, $method);
};

echo $greeting('John'); // "Hello John via GET"


for ($i = 0, $for_max = count($cached_inserts); $i < $for_max; $i++) {
    if ($smarty->debugging) {
        $_params = array();
        require_once(SMARTY_CORE_DIR . 'core.get_microtime.php');
    }
    $args = unserialize($insert_args[$i]); $name = $args['name'];

    if (isset($args['script'])) {
        if(!smarty_core_get_php_resource($_params, $smarty)) {
            return false;
        }
        $php_resource = $_params['php_resource'];

        if ($resource_type == 'file') {
            $smarty->_include($php_resource, true);
        } else {
            $smarty->_eval($php_resource);
        }
    }

    $params['results'] = substr_replace($params['results'], $replace, strpos($params['results'], $cached_inserts[$i]), strlen($cached_inserts[$i]));
    if ($smarty->debugging) {
        $_params = array();
        require_once(SMARTY_CORE_DIR . 'core.get_microtime.php');
        $smarty->_smarty_debug_info[] = array('type'      => 'insert',
                                              'exec_time' => smarty_core_get_microtime($_params, $smarty) - $debug_start_time);
    }
}

return $params['results'];

for ($i = 0, $for_max = count($cached_inserts); $i < $for_max; $i++) {
function doComplicatedThing() {
    for ($i = 0, $for_max = count($cached_inserts); $i < $for_max; $i++) {
        if ($smarty->debugging) {
            $_params = array();
            require_once(SMARTY_CORE_DIR . 'core.get_microtime.php');
        }
        $args = unserialize($insert_args[$i]); $name = $args['name'];

        if (isset($args['script'])) {
            if(!smarty_core_get_php_resource($_params, $smarty)) {
                return false;
            }
            $php_resource = $_params['php_resource'];

            if ($resource_type == 'file') {
                $smarty->_include($php_resource, true);
            } else {
                $smarty->_eval($php_resource);
            }
        }

        $params['results'] = substr_replace($params['results'], $replace, strpos($params['results'], $cached_inserts[$i]), strlen($cached_inserts[$i]));
        if ($smarty->debugging) {
            $_params = array();
            require_once(SMARTY_CORE_DIR . 'core.get_microtime.php');
            $smarty->_smarty_debug_info[] = array('type'      => 'insert',
                                                  'exec_time' => smarty_core_get_microtime($_params, $smarty) - $debug_start_time);
        }
    }

    return $params['results'];
}

Working Memory

Dogs, Strips of Bacon, Gina

3 dogs run into the your living room
Gina feeds each dog a strip of bacon
- except Spackle because he pooped on the floor earlier
Spot wags her tail looking at you then rolls over
You're hungry and eat 2 strips of bacon from the oven set at 400°F
Gina hands you fresh bacon and you drop it because it's too hot
- 5 pieces fall to the ground
- No more bacon
How many bacon strips were prepared today?
How many bacon strips were eaten today?

Dogs, Strips of Bacon, Gina

3 dogs run into the your living room
Gina feeds each dog 2 dogs a strip of bacon
- except Spackle because he pooped on the floor earlier
Spot wags her tail looking at you then rolls over
You're hungry and eat 2 strips of bacon from the oven set at 400°F
Gina hands you more bacon and you drop it because it's too hot
- 5 pieces fall to the ground
- No more bacon
How many bacon strips were prepared today?
How many bacon strips were eaten today?

Nested Control Structures :(


$users = User::all();

foreach ($users as $user) {
    if (is_admin($user)) {
        echo "ID: " . $user->id . " Name: " . $user->name . "
";
        
        foreach ($user->groups as $group) {
            if (!in_array($group->admin, $users)) {
                continue;
            }
            echo "Group Admin: " . $user->name . "
";
        }
    } else {
        foreach ($user->activities as $activity) {
            echo "Activities: ";
            if ($activity->isActive()) {
                echo $activity->name . "
";
            }
        }
    }
}

Control Structure Anxiety


foreach (...) {
    if (...) {
        foreach (...) {
            if (...) {
                // ...
            }
        }
    } else {
        foreach (...) {
            if (...) {
                // ...
            }
        }
    }
}

New rules?
New variables?
Minor details vs New contexts

Readability :(


$customFieldValues = $this->getRequestParam("customFieldValues");
if ($customFieldValues) {
    foreach ($customFieldValues as $custValueInfo) {
        $valueEntry = $reservation->getCustomFieldValueEntry($custValueInfo['id']);
        // Not found, this is the first time they're setting the value, so we need
        // to create a new entry
        if (!$valueEntry) {
            $customField = $resource->getCustomField($custValueInfo['id']);
            if (!$customField) {
                throw new \InvalidArgumentException("Attempted to set a custom field that does not belong to the specified Resource");
            }

            $valueEntry = new ReservationCustomFieldValueEntry();
            $valueEntry->setField($customField);
            $reservation->addCustomFieldValue($valueEntry);
        }

        $valueEntry->setValue($custValueInfo['value']);
    }
}

Local variables are noisy :(


public function getOldestStudentAction(Request $request) {
    $method = $request->getMethod();
    if ($method !== 'PUT') {
        throw new \BadRequestMethod('Endpoint only accepts PUT requests');
    }

    $db = $this->getDatabase()->getConnection();
    $roster = $db->query('Roster', $request->get('roster_id'));

    $oldest = null;
    foreach ($roster->getStudents() as $student) {
        if (!$oldest || $student->getAge() > $oldest->getAge()) {
            $oldest = $student;
        }
    }

    $oldestName = $oldest->getName();
    echo "The oldest student is " . $oldestName . "\n";
    $db->close();
    $roster->updateLastAccess();

    // $method, $db, $roster, $request, $oldest, $student, $oldestName
}

Ruthlessly Eliminate Local Variables


$method = $request->getMethod();
if ($method !== 'POST') {
    // ...
}


if ($request->getMethod() !== 'POST') {
    // ...
}

Chain Method Calls


$db = $this->getDatabase();
$conn = $db->getConnection();
$roster = $conn->query('Roster', $request->get('roster_id'));


$roster = $this
    ->getDatabase()
    ->getConnection()
    ->query('Roster', $request->get('roster_id'));

array ==> map ==> filter ==> reduce


// 1. Multiply by 2
// 2. Remove any results over 9
// 3. Add numbers together

$start = [1, 2, 3, 4, 5];

echo array_reduce(array_filter(array_map(function ($i) {
    return $i * 2;
}, $start), function ($i) {
    return $i < 9;
}), function ($sum, $i) {
    return $sum + $i;
}, 0);

// 20


array_map($fn, $array, [$...])
array_filter($array, $fn)
array_reduce($array, $fn, $initial)


$friends = ['John', 'Chris', 'Penelope', 'Megan'];

echo join(", ", addGreeting(keepUnderLength(6, $friends)));

// "Hello John, Hello Chris, Hello Megan"


$friends = ['John', 'Chris', 'Penelope', 'Megan'];

$short = keepUnderLength(6, $friends);
$greeted = addGreeting($short);
$result = join(", ", $greeted);

echo $result; // "Hello John, Hello Chris, Hello Megan"

Unix Pipes


$ cat friends.txt
John
Chris
Penelope
Megan


$ cat friends.txt | awk 'length($0) < 6'
John
Chris
Megan


$ cat friends.txt | awk 'length($0) < 6' | xargs -L1 echo "Hello"
Hello John
Hello Chris
Hello Megan

c/o Samantha Quiñones, "Building Real-Time Metric Pipelines"

Pipelines


$friends = new \Haystack\HArray(['John', 'Chris', 'Penelope', 'Megan']);
$greetings = $friends->filter(...)->map(...)->toArray();

// ["Hello John", "Hello Chris", "Hello Megan"]


class HArray extends \ArrayObject
{
    private $array = [];
    public function __construct(array $a = []) {
        $this->array = $a;
    }
    public function map(callable $func) {
        return new static(array_map($func, $this->array));
    }
    public function filter(callable $func = null) {
        return new static(array_filter($this->array, $func));
    }
    public function reduce(callable $func, $initial = null) {
        return array_reduce($this->array, $func, $initial);
    }
}

Pipelines


$friends = new \Haystack\HArray(['John', 'Chris', 'Penelope', 'Megan']);
$greetings = $friends
    ->filter(...)
    ->filter(...)
    ->map(...)
    ->reduce(...)
    ->toArray();

return $greetings;

Pipelines


$friends = new \Haystack\HArray(['John', 'Chris', 'Penelope', 'Megan']);
$greetings = $friends
    ->filter(function ($name) {
        return ...
    })
    ->filter(function ($name) {
        return ...
    })
    ->map(function ($name) {
        return ...
    })
    ->reduce(function ($name) {
        return ...
    })
    ->toArray();

return $greetings;

JavaScript ES6 Promises


get('story.json')
.then(function(response) {
    return JSON.parse(response);
})
.then(function(response) {
    console.log("Yey JSON!", response);
});

Path to Completion

Web Form Design: Filling in the Blanks

Luke Wroblewski

Pipelines


// 1. Multiply by 2
// 2. Remove any results over 9
// 3. Add numbers together

$start = [1, 2, 3, 4, 5];

echo (new \Haystack\HArray($start))
    ->map(function ($i) {
        return $i * 2;
    })
    ->filter(function ($i) {
        return $i < 9;
    })
    ->reduce(function ($sum, $i) {
        return $sum + $i;
    });

// 20

Refactor to Pipelines

Exercise: Find all classes to instantiate


$ tree /projects/loops/src
src
└── FizzBuzz
    ├── Canonical.php            class Canonical {}
    ├── Haystack.php             class Haystack {}
    └── SomeInterface.php        interface SomeInterface {}


kataProvider('FizzBuzz');
// [  "\\RethinkingLoops\\FizzBuzz\\Canonical",
//    "\\RethinkingLoops\\FizzBuzz\\Haystack" ]


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);
    $classes = [];
    foreach (scandir($src) as $filename) {
        // [  ".",
        //    "..",
        //    "Canonical.php",
        //    "Haystack.php",
        //    "SomeInterface.php" ]
    }

    return $classes;
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    $classes = [];
    foreach (scandir($src) as $filename) {
        $path = sprintf('%s/%s', $src, $filename);
        // [
        //     "/projects/loops/src/FizzBuzz/.",
        //     "/projects/loops/src/FizzBuzz/..",
        //     "/projects/loops/src/FizzBuzz/Canonical.php",
        //     "/projects/loops/src/FizzBuzz/Haystack.php",
        //     "/projects/loops/src/FizzBuzz/SomeInterface.php",
        // ]
    }

    return $classes;
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    $classes = [];
    foreach (scandir($src) as $filename) {
        $path = sprintf('%s/%s', $src, $filename);
        if (false === is_dir($path)) {
            // [
            //     "/projects/loops/src/FizzBuzz/Canonical.php",
            //     "/projects/loops/src/FizzBuzz/Haystack.php",
            //     "/projects/loops/src/FizzBuzz/SomeInterface.php",
            // ]
        }
    }

    return $classes;
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    $classes = [];
    foreach (scandir($src) as $filename) {
        $path = sprintf('%s/%s', $src, $filename);
        if (false === is_dir($path)) {
            $path = str_replace('.php', '', $path);
            // [
            //     "/projects/loops/src/FizzBuzz/Canonical",
            //     "/projects/loops/src/FizzBuzz/Haystack",
            //     "/projects/loops/src/FizzBuzz/SomeInterface",
            // ]
        }
    }

    return $classes;
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    $classes = [];
    foreach (scandir($src) as $filename) {
        $path = sprintf('%s/%s', $src, $filename);
        if (false === is_dir($path)) {
            $path = str_replace('.php', '', $path);
            $fqcn = str_replace($src . '/', '\\RethinkingLoops\\' . $dir . '\\', $path);
            // [
            //     "\\RethinkingLoops\\FizzBuzz\\Canonical",
            //     "\\RethinkingLoops\\FizzBuzz\\Haystack",
            //     "\\RethinkingLoops\\FizzBuzz\\SomeInterface",
            // ]
        }
    }

    return $classes;
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    $classes = [];
    foreach (scandir($src) as $filename) {
        $path = sprintf('%s/%s', $src, $filename);
        if (false === is_dir($path)) {
            $path = str_replace('.php', '', $path);
            $fqcn = str_replace($src . '/', '\\RethinkingLoops\\' . $dir . '\\', $path);

            $r = new \ReflectionClass($fqcn);
            if (false === $r->isAbstract()) {
                $classes[] = $fqcn;
            }
            // [ "\\RethinkingLoops\\FizzBuzz\\Canonical",
            //   "\\RethinkingLoops\\FizzBuzz\\Haystack" ]
        }
    }

    return $classes;
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    $classes = [];
    foreach (scandir($src) as $filename) {
        $path = sprintf('%s/%s', $src, $filename);
        if (false === is_dir($path)) {
            $path = str_replace('.php', '', $path);
            $fqcn = str_replace($src . '/', '\\RethinkingLoops\\' . $dir . '\\', $path);

            $r = new \ReflectionClass($fqcn);
            if (false === $r->isAbstract()) {
                $classes[] = $fqcn;
                // $dir, $src, $classes, $filename, $path, $fqcn, $r
            }
        }
    }

    return $classes;
}

Refactor to array_*


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    $paths = array_map(function ($filename) use ($src) {
        return sprintf('%s/%s', $src, $filename);
    }, scandir($src));

    $files = array_filter($paths, function ($path) {
        return false === is_dir($path);
    });

    $allClasses = array_map(function ($path) use ($src, $dir) {
        $path = str_replace('.php', '', $path);
        return str_replace($src . '/', '\\RethinkingLoops\\' . $dir . '\\', $path);
    }, $files);

    return array_filter($allClasses, function ($class) {
        return false === (new \ReflectionClass($fqcn))->isAbstract();
    });
}

Refactor to Pipeline


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    return (new \Haystack\HArray(scandir($src)))
        // [
        //    ".",
        //    "..",
        //    "Canonical.php",
        //    "Haystack.php",
        //    "SomeInterface.php",
        // ]
}


function kataProvider($dir)
{
    $src = realpath(__DIR__ . '/../src/' . $dir);

    return (new \Haystack\HArray(scandir($src)))
        ->map(function ($filename) use ($src) {
            return sprintf('%s/%s', $src, $filename);
        })
        // [
        //     "/projects/loops/src/FizzBuzz/.",
        //     "/projects/loops/src/FizzBuzz/..",
        //     "/projects/loops/src/FizzBuzz/Canonical.php",
        //     "/projects/loops/src/FizzBuzz/Haystack.php",
        //     "/projects/loops/src/FizzBuzz/SomeInterface.php",
        // ]
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    return (new \Haystack\HArray(scandir($src)))
        ->map(function ($filename) use ($src) {
            return sprintf('%s/%s', $src, $filename);
        })
        ->filter(function ($path) {
            return false === is_dir($path);
        })
        // [
        //     "/projects/loops/src/FizzBuzz/Canonical.php",
        //     "/projects/loops/src/FizzBuzz/Haystack.php",
        //     "/projects/loops/src/FizzBuzz/SomeInterface.php",
        // ]
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    return (new \Haystack\HArray(scandir($src)))
        ->map(function ($filename) use ($src) {
            return sprintf('%s/%s', $src, $filename);
        })
        ->filter(function ($path) {
            return false === is_dir($path);
        })
        ->map(function ($filepath) use ($src, $dir) {
            $filepath = str_replace('.php', '', $filepath);
            return str_replace($src . '/', '\\RethinkingLoops\\' . $dir . '\\', $filepath);
        })
        // [ "\\RethinkingLoops\\FizzBuzz\\Canonical",
        //   "\\RethinkingLoops\\FizzBuzz\\Haystack",
        //   "\\RethinkingLoops\\FizzBuzz\\SomeInterface" ]
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    return (new \Haystack\HArray(scandir($src)))
        ->map(function ($filename) use ($src) {
            return sprintf('%s/%s', $src, $filename);
        })
        ->filter(function ($path) {
            return false === is_dir($path);
        })
        ->map(function ($filepath) use ($src, $dir) {
            $filepath = str_replace('.php', '', $filepath);
            return str_replace($src . '/', '\\RethinkingLoops\\' . $dir . '\\', $filepath);
        })
        ->filter(function ($fqcn) {
            return false === (new \ReflectionClass($fqcn))->isAbstract();
        })
        ->toArray();
        // [ "\\RethinkingLoops\\FizzBuzz\\Canonical",
        //   "\\RethinkingLoops\\FizzBuzz\\Haystack" ]
}


function kataProvider($dir) {
    $src = realpath(__DIR__ . '/../src/' . $dir);

    return (new \Haystack\HArray(scandir($src)))
        ->map(function ($filename) use ($src) {
            return sprintf('%s/%s', $src, $filename);
        })
        ->filter(function ($path) {
            return false === is_dir($path);
        })
        ->map(function ($filepath) use ($src, $dir) {
            $filepath = str_replace('.php', '', $filepath);
            return str_replace($src . '/', '\\RethinkingLoops\\' . $dir . '\\', $filepath);
        })
        ->filter(function ($fqcn) {
            return false === (new \ReflectionClass($fqcn))->isAbstract();
        })
        ->toArray();
}

Available Today!

transducers-php


use Transducers as t;

$xf = t\comp(
    t\drop(2),
    t\map(function ($x) { return $x + 1; },
    t\filter(function ($x) { return $x % 2; },
    t\take(3)
);

$data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
$result = t\xform($data, $xf); // [5, 7, 9]

PHP RFC: Arrow Functions


$elements = [1, 3, 5];

// live
$result = array_map(function($x) { return $x * 2; }, $elements);
 
// proposed
$result = array_map(function($x) => $x * 2, $elements);

PHP RFC: Arrow Functions


$friends = new \Haystack\HArray(['John', 'Chris', 'Penelope', 'Megan']);

$greetings = $friends
    ->filter(function ($name) => strlen($name) < 6)
    ->map(function ($name) => 'Hello ' . $name);

echo join(", ", $greetings->toArray());
// "Hello John, Hello Chris, Hello Megan"

Rethinking Loops Playground


$ composer create-project johnkary/rethinking-loops

Reading List


(defn encode
  [#^InputStream input #^Writer output #^String alphabet line-length]
  (let [buffer (make-array Byte/TYPE 3)]
    (loop [line 0]
      (let [len (.read input buffer)]
        (when (pos? len)
          (let [b0 (Integer/valueOf (int (aget buffer 0)))
                b1 (Integer/valueOf (int (aget buffer 1)))
                b2 (Integer/valueOf (int (aget buffer 2)))]
            (cond (= len 3)
                  (let [s0 (bit-and 0x3F (bit-shift-right b0 2))
                        s1 (bit-and 0x3F
                                    (bit-or (bit-shift-left b0 4)
                                            (bit-shift-right b1 4)))
                        s2 (bit-and 0x3F
                                    (bit-or (bit-shift-left b1 2)
                                            (bit-shift-right b2 6)))
                        s3 (bit-and 0x3F b2)]
                    (.append output (.charAt alphabet s0))
                    (.append output (.charAt alphabet s1))
                    (.append output (.charAt alphabet s2))
                    (.append output (.charAt alphabet s3))))))))))


$list = [2, 4, 6, 8, 10];

for ($i=0; $i < count($start); $i++) {
    $current = $start[$i];
    $end[] = $current * 2;
}

foreach ($list as $idx => $value) {
    echo $value;
    unset($list[$idx]);
}

Bugs cannot exist
in code that doesn't exist

Be Expressive

Thanks.

Source Material Credits

Questions?

John Kary • @johnkary

Slides: http://johnkary.net/talks
Feedback: https://joind.in/talk/bad7e

Rethinking Loops by John Kary is licensed under a
Creative Commons Attribution-ShareAlike 4.0 International License.

Performance

Arrays vs Objects Benchmarks (5.6, 7.0)
http://bit.ly/rethinking-loops-perf-1
Why objects (usually) use less memory than arrays in PHP
http://bit.ly/rethinking-loops-perf-2

Why Arrays?

Quantity	One	Arrays
NULL	null	[]
0	null	[]
1	new User()	[new User()]
3	:(	[ new User(), new User(), new User(), ]
a lot	:(	[...]

Why Arrays?


/** @param User[]|User|null $users */
function findUserGroups($users) {
    if ($users === null) return null;

    if ($users instanceof User) {
        $groups = Group::findByUser($users->id);
        return $groups;
    }

    if (count($users) === 0) {
        return [];
    } else {
        $groups = [];
        foreach ($users as $user) {
            $userGroups = Group::findByUser($user->id);
            if (!$groups) continue;
            $groups = array_merge($groups, $userGroups);
        }
    }

    return $groups;
}

Why Arrays?


/** @param User[]|User|null $users */
function findUserGroups($users) {
    $groups = [];

    foreach ((array) $users as $user) {
        $userGroups = Group::findByUser($user->id);
        if (!$groups) continue;
        $groups = array_merge($groups, $userGroups);
    }

    return $groups;
}

Why Arrays?


/** @param User[]|User|null $users */
function findUserGroups($users) {
    $groups = [];

    foreach ((array) $users as $user) {
        $groups = array_merge($groups, (array) Group::findByUser($user->id));
    }

    return $groups;
}

Why Arrays?


function findUserGroups($users) {
    return array_reduce((array) $users, function ($groups, $user) {
        return array_merge($groups, (array) Group::findByUser($user->id));
    }, []);
}

Rethinking Loops

FizzBuzz

array_map

array_filter

array_reduce

Expressive Language

Cool

Cool

Expressive Code

array_map

array_filter

array_reduce

Defining a global function

Defining a static function

Defining an object method

Defining anonymous functions

Scope

Scope

Scope

Scope

Scope

Working Memory

Dogs, Strips of Bacon, Gina

Dogs, Strips of Bacon, Gina

Nested Control Structures :(

Control Structure Anxiety

Readability :(

Local variables are noisy :(

Ruthlessly Eliminate Local Variables

Chain Method Calls

array ==> map ==> filter ==> reduce

Unix Pipes

Pipelines

Pipelines

Pipelines

JavaScript ES6 Promises

Path to Completion

Web Form Design: Filling in the Blanks

Luke Wroblewski

Pipelines

Refactor to Pipelines

Exercise: Find all classes to instantiate

Refactor to array_*

Refactor to Pipeline

Available Today!

transducers-php

PHP RFC: Arrow Functions

PHP RFC: Arrow Functions

Rethinking Loops Playground

Reading List

Bugs cannot existin code that doesn't exist

Be Expressive

Thanks.

Source Material Credits

Questions?

Performance

Why Arrays?

Why Arrays?

Why Arrays?

Why Arrays?

Why Arrays?

:)

Bugs cannot exist
in code that doesn't exist