ps/fluent-traversable

Support for operating on collections and arrays by functional way. Inspired by guava's FluentIterable, java8 Stream framework and scala stuff

0.3.2 2014-11-11 17:35 UTC

README

Build Status

FluentTraversable is small tool that adds a bit of functional programming to php, especially for arrays and collections. This library is inspired by java8 stream framework, guava FluentIterable and Scala functional features. To fully enjoy of this library, knowledge of basic functional patterns is welcome.

Summary and key features:

  • allows to working with arrays and everything that implements Traversable interface
  • based on functional programming concepts:
  • simplifies algorithms' code. Lets see few code examples and try to rewrite that examples using loops and ifs:
  • makes code more declarative, readable, less complex and more maintainable
  • simple, considered interface: 95% of methods with 0 or 1 argument, 5% of methods with 2 arguments, 0% of methods with 3 or more arguments
  • no magic in implementation, full support for IDE code completion
  • inspired by few other technologies, but fully adapted to php world. This library is not a blind copy of other tools.
  • framework independent, only 1 small external dependency - php-option. This library won't download a half of internet.

Quick example

We have an array of patients and we want to know percentage of female patients grouped by blood type.


    $patients = array(...);
    
    $info = FluentTraversable::from($patients)
        ->groupBy(get::value('bloodType'))
        ->map(
            FluentComposer::forArray()
                ->partition(is::eq('sex', 'female'))
                ->map(func::unary('count'))
                ->collect(function($elements){
                    list($femalesCount, $malesCount) = $elements;
                    return $femalesCount / ($femalesCount + $malesCount) * 100;
                })
        )
        ->toMap();

Explanation and more information about this example you get here.

ToC

  1. Installation
  2. FluentTraversable
  3. FluentComposer
    1. FluentComposer as predicate / mapping function
  4. Predicates
  5. Puppet
  6. Contribution
  7. License

Installation

Installation is very easy (thanks to composer ;)):

(add to require section in your composer.json file)

"ps/fluent-traversable": "*"

You should choose last stable version, wildcard char ("*") is only an example.

FluentTraversable

Thanks to FluentTraversable class you can operate on arrays and collection in declarative and readable way. There is a simple example.

We want to get emails of male authors of books that have been released before 2007.


    $books = array(/* some books */);
    
    $emails = array();
    
    foreach($books as $book) {
        if($book->getReleaseDate() < 2007) {
            $authors = $book->getAuthors();
            foreach($authors as $author) {
                if($author->getSex() == 'male' && $author->getEmail()) {
                    $emails[] = $author->getEmail();
                }
            }
        }
    }

Ok, nested loops, nested if statements... It doesn't look good. If I use php array_map and array_filter functions, result wouldn't be better, would be even worst, so I omit this example.

The same code using FluentTraversable:


    //some imports
    use FluentTraversable\FluentTraversable;
    use FluentTraversable\Semantics\is;
    use FluentTraversable\Semantics\get;

    $books = array(/* some books */);
    
    $emails = FluentTraversable::from($books)
        ->filter(is::lt('releaseDate', 2007))
        ->flatMap(get::value('authors'))
        ->filter(is::eq('sex', 'male'))
        ->map(get::value('email'))
        ->filter(is::notNull())
        ->toArray();       

IMPORTANT

In examples toMap and toArray functions are used to convert elements to array. The difference between those two functions is toArray re-indexes elements, toMap preserves indexes. You should use toArray method when indexes in your use case are not important, otherwise you should use toMap.

There are no loops, if statements, it looks straightforward, flow is clear and explicit (when you now what filter, flatMap, map etc methods are doing - as I said before the basics functional programming patters are needed ;)).

IMPORTANT

What does flatMap do? It maps single values to collections of values and then merges all those collections into one collection. In example above Book has many authors, thanks to flatMap we are able to extract all authors to one dimensional array. When we would use map, on output would be array of authors' arrays.

is class (alias to Predicates class) is factory for closures that have one argument and evaluate it to boolean value. There are lt, gt, eq, not etc methods. Closures in php are very lengthy, you have to write function keyword, curly braces, return statement, semicolon etc - a lot of syntax noise. Closure is multiline (yes, I now it can be written in single line, but it would be unreadable), so it is no very compact. To handle simple predicate cases, you might use is class. More about predicates you can read in Predicates section.

get::value('authors') also is a shortcut for closures, this is semantic equivalent to:


    function($object){
        return $object->getAuthors();
    }

Nested paths in predicates and get::value function are supported, so this code works as expected: get::value('address.city.name').

IMPORTANT

In the most of functions (where make it sense) to predicate/mapping function are provided two arguments: element value and index:

    FluentTraversable::from(array('a' => 'A', 'b' => 'B'))
        ->map(function($value, $index){
            return $value.$index;
        })
        ->toMap();
        //result will be: array('a' => 'Aa', 'b' => 'Bb')

When you won't index to be passed as second argument, you could use func::unary($func) function. It is very helpful especially when you want to use php build-in function that has optional second argument with different meaning, for example str_split:

    FluentTraversable::from(array('some', 'values'))
        ->flatMap(func::unary('str_split'))
        ->toArray();
        //result will be: array('s', 'o', 'm', 'e', 'v', 'a', 'l', 'u', 'e')

FluentTraversable has a lot of useful methods: map, flatMap, filter, unique, groupBy, orderBy, allMatch, anyMatch, noneMatch, firstMatch, maxBy, minBy, reduce, toArray, toMap and more. List, description and examples of all those methods are available in TraversableFlow interface. Each method belongs to one of two groups: intermediate or terminate operations. Intermediate operation does some work on input array, modifies it and returns FluentTraversable object for further processing, so you can chain another operation. Terminate operation does some calculation on each element of array and returns result of this calculation. For example size operation returns integer that is length of input array, so you can not chain operation anymore.

Example:


    FluentTraversable::from(array())
        ->filter(...)//intermediate operation, so I can chain
        ->map(...)//intermediate operation, so I can chain
        ->size()//terminate operation, I cannot chain - it returns integer

There are few terminal operations that returns Option value (if you don't know what is Option or Optional value pattern, follow this links: php-option, Optional explanation in Java). For example firstMatch method could find nothing, so instead return null or adding second optional argument to provide default value, Option object is returned. Option object is a wrapper for value, it can contain value, but it haven't to. You should threat Option as collection with 0 or 1 value. Option class provides few familiar methods to FluentTraversable, for example map and filter. You can get value from Option by getOrElse method:

Example:


    FluentTraversable::from($books)
        ->firstMatch(is::eq('author.name', 'Stephen King'))
        //there is Option instance, you can transform value (thanks to map) if this value exists
        ->map(function($book){
            return 'Found book: '.$book->getTitle();
        })
        //provide default value if book wasn't found
        ->orElse(Option::fromValue('Not found any book...'))
        //print result to stdout thanks to Option::map method
        ->map('printf')
        //or you can call "->get()" and assign to variable, it is safe because you provided default value by "orElse"
        ;

If Stephen King's book was found, "Found book: TITLE" will be printed, otherwise "Not found any book...".

Properly used, option is very powerful and it integrates with FluentTraversable perfectly. Option::map method is very inconspicuous, but it is also very useful. Thanks to Option::map you can execute piece of code when value is available without using if statement:


    FluentTraversable::from($books)
        ->maxBy(get::value('rating'))
        ->map(function(Book $book){
            $this->takeToBackpack($book);
        });

IMPORTANT

Option in many cases is very useful and it often simplifies the code. If you do not feel how to properly use it, check "Bigger example" section in this article and all examples with Option in this documentation. Option has getOrElse method, so you can eventually use it to grab the value or default value. However I recommend you to learn how to properly use this pattern, in literature it is also called Maybe or Optional pattern.

IMPORTANT

When you want to use Option::map function, be aware when provided mapping function returns null, map function will return Some(null) (not None()) - that could be undesirable. Example below is not correct if $patientRepo::find() method might return null:

Option::fromValue($patientId)
  ->map([$patientRepo,'find'])
  //there could be `Some(null)` value! 
  ->map(get::value('doctor.phone'))
  //there could be also `Some(null)` value, so `null` might be passed to `$this::callToDoctor`
  ->each([$this,'callToDoctor']);

When you want to transform value wrapped by Option and mapping function could return null you should use flatMap and get::option() combo. There is correct example:

Option::fromArrayValue($patientId)
  ->flatMap(get::option([$patientRepo,'find']))
  //when `$this::callToDoctor` return `null` there will be `None`
  ->flatMap(get::option('doctor.phone'))
  //when doctor has not phone set, there will be `None` value
  ->each([$this,'callToDoctor']);

get::option is similar to get::value, the difference is it wraps value in Option type.

FluentComposer

FluentComposer is a tool to compose complex operations on arrays. You can define one complex operation thanks to composer, and apply it multiple times on any array. FluentComposer has the same interface as FluentTraversable (those two classes implements the same interface: TraversableFlow).

There is an example:


    $maxEvenPrinter = FluentComposer::forArray();

    //very important is, to not chain directly from `forArray()` method, first you should assign created object
    //to variable, and then using reference to object you can compose your function

    $maxEvenPrinter
        ->filter(function($number){
            //only even numbers
            return $number % 2 === 0;
        })
        ->max()
        //"max" (as same as firstMatch) returns Option, because there is possibility given array is empty
        ->map(function($value){
            return 'max even number: '.$value;
        })
        ->orElse(Option::fromValue('max even number not found'))
        ->map('printf');

Ok, we have $maxEvenPrinter object, what's next?


    $maxEvenPrinter(array(1, 3, 5, 2, 4));
    //output will be: "max even number: 4"
    
    $maxEvenPrinter(array(1, 3, 5));
    //output will be: "max even number not found"

As I said, FluentComposer has almost the same methods as FluentTraversable. The difference between those two classes is that, FluentTraversable needs input array when object is created and it should be used once, FluentComposer doesn't need array when object is created and can be invoked multiple times with different input arrays. Internally FluentComposer uses FluentTraversable instance ;) You should threat FluentComposer as tool to compose functions.

FluentComposer has three factory methods that differ in arguments that are accepted by created function:

  • FluentComposer::forArray() - created function accepts one array/traversable argument

    
        $func = FluentComposer::forArray();
        $func-> /* some chaining methods */;
            
        $func(array('value1', 'value2', 'value3'));
    
  • FluentComposer::forVarargs() - created function accepts variable number of arguments (varargs):

    
        $func = FluentComposer::forVarargs();
        $func-> /* some chaining methods */;
        
        $func('value1', 'value2', 'value3');
    
  • FluentComposer::forValue() - created function accepts one argument that will be threaten as only element of array. This method is similar to FluentComposer::forVarargs(), the difference is all arguments are ignored except the first.

    
        $func = FluentComposer::forValue();
        $func-> /* some chaining methods */;
    
        $func('value1', 'this value will be ignored')
    

FluentComposer as predicate / mapping function

You can use FluentComposer to create predicate or mapping function for FluentTraversable, especially after functions that transforms single value to array of values (groupBy, partition etc.).

Example:

We have an array of patients and we want to know percentage of female patients grouped by blood type.


    $patients = array(...);
    
    $info = FluentTraversable::from($patients)
        ->groupBy(get::value('bloodType'))
        //we have multi-dimensional array, where key is bloodType, value is array of patients
        ->map(
            //we map array of patients for each blood type to percentage value, so lets compose a function
            FluentComposer::forArray()
                //split array of patients into two arrays, first females, second males
                ->partition(is::eq('sex', 'female'))
                //map those arrays to its size, so we have number of females and males
                ->map(func::unary('count'))
                //calculate a percent
                ->collect(function($elements){
                    list($femalesCount, $malesCount) = $elements;
                    return $femalesCount / ($femalesCount + $malesCount) * 100;
                })
        )
        //get our result with index preserving 
        ->toMap();

IMPORTANT

Directly chaining from FluentComposer::forArray() (and other factory methods) is not always safe, some methods does not return FluentComposer, but Option object. Methods that returns Option are: reduce, firstMatch, max, min, first, last, get. When you after all want to chain directly from FluentComposer::forArray() and use terminal operation that returns Option, you can apply a trick:


  ->map(
      $f = FluentComposer::forArray(), $f
           ->firstMatch(is::eq('name', 'Stefan'))
           ->getOrElse('Not found')
  )

There is also FluentComposer::forValue() method to create function with one argument that contains single value. It might be useful to create predicates or mapping functions for single value.

Example:

We want to find doctors that all patients are women (gynecologists?).

    
    $doctors = array(/* some doctors */);

    $doctors = FluentTraversable::from($doctors)
        ->filter(
            FluentComposer::forValue()
                ->flatMap(get::value('patients'))
                ->allMatch(is::eq('sex', 'female'))
        )
        ->toArray();

Predicates

Predicate is a function that evaluates single value to boolean. Predefined predicates are available in is and Predicates classes. Those classes are the same, is is an alias to Predicates, so you can choose witch one to use (is gives more expressiveness to code). Predicates are perfect to use in filter, firstMatch, partition, allMatch, noneMatch, anyMatch methods of FluentTraversable.

The most of predicates (for example: eq, notEq, gt, qte, identical, notIdentical, in, notIn, contains) have two versions:

  • unary: predicate($valueToCompare)

    
        $gt25 = is::gt(25);    
        $gt25(26);//evaluates to true
    
  • binary - predicate($property, $valueToCompare)

    
        $ageGt25 = is::gt('age', 25);
        $gt25(array('age', 26));//evaluates to true
    

Few predicates (null, notNull, false, true, blank, notBlank) have also two, but different versions:

  • not argument: predicate()

    
        $true = is::true();    
        $true(true);//evaluates to true
    
  • unary: predicate($property)

    
        $true = is::true('awesome');    
        $true(array('awesome' => true));//evaluates to true
    

There are also logical predicates (not, allTrue - logical and, anyTrue - logical or), but when you need to create complex predicate maybe the better and more readable way is just to use closure. allTrue and anyTrue accepts also evaluated values, for example:


    $alwaysFalse = is::allTrue(false, is::eq(25));
    $alwaysTrue = is::anyTrue(true, is::eq(25));

Evaluated values could be useful when filtering of some values depends on external condition and you don't want to use separate if statement because of readability purpose - of course if your array is really big, be aware the iteration through all elements will be done, so be carefully and use that feature consciously.

IMPORTANT

Predicates can also be used with grouping functions. Now there is only size::of() function.

Example:

We want to find doctors with less than 5 patients


    $doctors = array(...);
    
    $doctors = FluentTraversable::from($doctors)
        ->filter(is::lt(size::of('patients'), 5))
        ->toArray();

Puppet

Puppet is a very small (less than 100 lines of code) class, but it is also very powerful. What is a Puppet? Thanks to Puppet you can "record" some behaviour and execute this behaviour multiple times on various objects.

Example:


    $book = ...;
    $puppet = Puppet::record()->getPublisher()->getName();
    
    echo $puppet($book);//$book->getPublisher()->getName() will be invoked

Puppet supports property access, array access and method calls with arguments. Originally it was created to simplify map and flatMap operations in FluentTraversable. It is is also used internally by FluentComposer, but maybe you will find another use case for Puppet.

Puppet has two factory methods: record and object - those methods are the same, object method was created only for semantic purpose. You can use Puppet to create mapping function for map, flatMap etc. functions, but get::value() is recommended for this purpose.

the class is alias to Puppet, it only adds semantic meaning to using Puppet in FluentTraversable context: ->map(the::object()->getName()) is much more readable than ->map(Puppet::record()->getName()).

Contribution

Any suggestions, PR, bug reports etc. are welcome ;)

License

MIT - details in LICENSE file