Toru 取る

Toru is a standalone tool for iterable collections, ready for simple day-to-day tasks and advanced optimizations.
Most of its functionality is based on native generators for efficiency with large data sets.

💿 composer require dakujem/toru

📒 Changelog

Toru provides a few common

• iteration primitives (e.g. map, filter, tap),
• aggregates (e.g. reduce, search, count)
• and utility functions (e.g. chain, valuesOnly, slice, limit)

... implemented using generators.

TL;DR:

• transform elements of native iterable type* collections (iterators and arrays) without converting to arrays
• keys (indexes) provided for every mapper, filter, reducer or effect function
• fluent call chaining enabled (Lodash-style)
• lazy per-element evaluation of transformations
• transform large data sets without increasing memory usage
• better memory efficiency of generators compared to native array functions
• slower than native array functions or direct transformations inside a foreach block

* The iterable is a built-in compile time type alias for array|Traversable encompassing all arrays and iterators, so it's not exactly a native type, technically speaking.

Fluent call chaining enables neat transformation composition.

_dash($collection)
    ->filter(predicate: $filterFunction)
    ->map(values: $mapperFunction)
    ->chain($moreElements)
    ->valuesOnly();

Toru enables memory-efficient operations on large data sets, because it leverages generators, which work on per-element basis and do not allocate extra memory.

// no extra memory wasted on creating a filtered array
$filtered = Itera::filter(input: $hugeDataSet, predicate: $filterFunction);
foreach($filtered as $key => $value){ /* ... */ }

All callable parameters always receive keys along with values.
This is a key advantage over native functions like array_map, array_reduce, array_walk, or array_filter.

$addresses = [
    'john.doe@example.com' => 'John Doe',
    'jane.doe@example.com' => 'Jane Doe',
];
$recipients = Itera::map(
    $addresses, 
    fn($recipientName, $recipientAddress) => new Recipient($recipientAddress, $recipientName),
);
Mailer::send($mail, $recipients);

🥋
The package name comes from Japanese word "toru" (取る), which may mean "to take", "to pick up" or even "to collect".

Examples

Task: Iterate over multiple large arrays (or other iterable collections) with low memory footprint:

use Dakujem\Toru\Itera;

// No memory wasted on creating a compound array. Especially true when the arrays are huge.
$all = Itera::chain($collection1, $collection2, [12,3,5], $otherCollection);

foreach ($all as $key => $element) {
    // do not repeat yourself
}

Task: Filter and map a collection, also specifying new keys (reindexing):

use Dakujem\Toru\Dash;

$mailingList = Dash::collect($mostActiveUsers)
    ->filter(
        predicate: fn(User $user): bool => $user->hasGivenMailingConsent()
    )
    ->adjust(
        values: fn(User $user) => $user->fullName(),
        keys: fn(User $user) => $user->emailAddress(),
    )
    ->limit(100);

foreach ($mailingList as $emailAddress => $recipientName) {
    $mail->addRecipient($emailAddress, $recipientName);
}

Task: Create a list of all files in a directory as path => FileInfo pairs without risk of running out of memory:

$files = _dash(
        new \RecursiveIteratorIterator(new \RecursiveDirectoryIterator($dir))
    )                                                                   // recursively iterate over a dir
    ->filter(fn(\SplFileInfo $fileInfo) => !$fileInfo->isDir())         // reject directories
    ->reindex(fn(\SplFileInfo $fileInfo) => $fileInfo->getPathname());  // index by full file path

Note that here we use global function _dash, which you may optionally define in your project. See the "Using a global alias" section below.

Usage

Most of the primitives described in API section below are implemented in 3 forms:

1. as a static method Itera::*(iterable $input, ...$args), for simple cases
2. as a fluent method of the Dash wrapper, Dash::*(...$args): Dash, best suited for fluent composition
3. as a factory method that creates partially applied callables IteraFn::*(...$args): callable, to be composed into pipelines or used as filters (i.e. in Twig, Blade, Latte, ...)

Example of filtering and mapping a collection, then appending some more already processed elements.

Usage of the individual static methods:

use Dakujem\Toru\Itera;

$filtered = Itera::filter(input: $collection, predicate: $filterFunction);
$mapped = Itera::apply(input: $filtered, values: $mapperFunction);
$merged = Itera::chain($mapped, $moreElements);
$processed = Itera::valuesOnly(input: $merged);

Usage of the Dash wrapper for fluent call chaining:

use Dakujem\Toru\Dash;

$processed = Dash::collect($collection)
    ->filter(predicate: $filterFunction)
    ->apply(values: $mapperFunction)
    ->chain($moreElements)
    ->valuesOnly();

Usage of the partially applied methods:

use Dakujem\Toru\Pipeline;
use Dakujem\Toru\IteraFn;

$processed = Pipeline::through(
    $collection,
    IteraFn::filter(predicate: $filterFunction),
    IteraFn::apply(values: $mapperFunction),
    IteraFn::chain($moreElements),
    IteraFn::valuesOnly(),
);

The $processed collection can now be iterated over. All the above operations are applied at this point only, on per-element basis.

foreach ($processed as $value) {
    // The filtered and mapped values from $collection will appear here,
    // followed by the elements present in $moreElements.
}

API

Chaining multiple iterables: chain, append

use Dakujem\Toru\Dash;
use Dakujem\Toru\Itera;
use Dakujem\Toru\IteraFn;

Itera::chain(iterable ...$input): iterable

// `append` is only present in `Dash` and `IteraFn` classes as an alias to `chain`
Dash::append(iterable ...$more): Dash
IteraFn::append(iterable ...$more): callable

The chain method creates an iterable composed of all the arguments.
The resulting iterable will yield all values (preserving keys) from the first iterable, then the next, then the next, and so on.

Compared to array_replace (or array_merge or the union operator + on arrays) this is very memory efficient, because it does not double the memory usage.

The append method appends iterables to the wrapped/input collection. It is an alias of the chain method.

The append method is present in IteraFn and Dash classes only. Appending makes no sense in the static context of the Itera class as there is nothing to append to.
In static context, use Itera::chain instead.

Mapping: map, adjust, apply, reindex, unfold

use Dakujem\Toru\Itera;

Itera::adjust(iterable $input, ?callable $values = null, ?callable $keys = null): iterable
Itera::apply(iterable $input, callable $values): iterable
Itera::map(iterable $input, callable $values): iterable
Itera::reindex(iterable $input, callable $keys): iterable
Itera::unfold(iterable $input, callable $mapper): iterable

The adjust method allows to map both values and keys.
The apply method maps values only,
and the reindex method allows mapping keys (indexes).

Do not confuse the map method with the native array_map, the native function has different interface. Instead, prefer to use the apply method to map values. The map method is an alias of the apply method.

For each of these methods, all mapping callables receive the current key as the second argument.
The signature of the mappers is always

fn(mixed $value, mixed $key): mixed

The unfold methods allows mapping and/or flattening matrices one level.
One niche trick to map both values and keys using a single callable with unfold is to return a single key-value pair (an array containing a single element with a specified key), like so:

use Dakujem\Toru\Itera;

Itera::unfold(
    [1,2,3,4],
    fn($value, $key) => ['double value for key ' . $key => $value * 2],
)

// or "produce new index and key based on the original value"
Itera::unfold(
    ['one:1', 'two:2', 'three:3'],
    function(string $value) {
        [$name, $index] = split(':', $value); // there could be a fairly complex regex here
        return [$index => $name];
    },
)

Reducing: reduce

This is an aggregate function, it will immediately consume the input.

Similar to array_reduce, but works with any iterable and passes keys to the reducer.

use Dakujem\Toru\Itera;

Itera::reduce(iterable $input, callable $reducer, mixed $initial): mixed

The reducer signature is

fn(mixed $carry, mixed $value, mixed $key): iterable|mixed

When using the Dash::reduce fluent call, the result is treated in two different ways:

1. when an iterable value is returned, the result is wrapped into a new Dash instance to allow to continue the fluent call chain (useful for matrix reductions)
2. when other mixed value type is returned, the result is returned as-is

use Dakujem\Toru\Dash;

// The value is returned directly, because it is not iterable:
Dash::collect([1,2,3])->reduce(fn() => 42); // 42

// The value `[42]` is iterable, thus a new `Dash` instance is returned:
Dash::collect([1,2,3])->reduce(fn() => [42])->count(); // 1

Filtering: filter

Create a generator that yields only the items of the input collection that the predicate returns truthy for.

use Dakujem\Toru\Itera;

Itera::filter(iterable $input, callable $predicate): iterable

Accept and eliminate elements based on a callable predicate.
When the predicate returns truthy, the element is accepted and yielded.
When the predicate returns falsy, the element is rejected and skipped.

The predicate signature is

fn(mixed $value, mixed $key): bool

Similar to array_filter, iter\filter.

Sidenote

Native CallbackFilterIterator may be used for similar results:

new CallbackFilterIterator(Itera::toIterator($input), $predicate)

Searching: search, searchOrFail, firstValue, firstKey, firstValueOrDefault, firstKeyOrDefault

These are aggregate functions, they will immediately consume the input.

use Dakujem\Toru\Itera;

Itera::search(iterable $input, callable $predicate, mixed $default = null): mixed
Itera::searchOrFail(iterable $input, callable $predicate): mixed
Itera::firstValue(iterable $input): mixed
Itera::firstKey(iterable $input): mixed
Itera::firstValueOrDefault(iterable $input, mixed $default = null): mixed
Itera::firstKeyOrDefault(iterable $input, mixed $default = null): mixed

Search for the first element that the predicate returns truthy for.

search returns the default value if no matching element is found, while searchOrFail throws.

The firstKey and firstValue methods throw when an empty collection is on the input, while the *OrDefault variants return the specified default value in such a case.

The predicate signature is

fn(mixed $value, mixed $key): bool

Slicing: slice, limit, omit

use Dakujem\Toru\Itera;

Itera::limit(iterable $input, int $limit): iterable
Itera::omit(iterable $input, int $omit): iterable
Itera::slice(iterable $input, int $offset, int $limit): iterable

Limit the number of yielded elements with limit, skip certain number of elements from the beginning with omit, or use slice to combine both omit and limit into a single call.
Keys will be preserved.

Passing zero or negative value to $limit yields an empty collection,
passing zero or negative values to $omit/$offset yields the full set.

Note that when omitting, the selected number of elements ($omit/$offset) is still iterated over but not yielded.

Similar to array_slice, preserving the keys.

Note:
Unlike array_slice, the keys are always preserved. Use Itera::valuesOnly when dropping the keys is desired.

Alterations: valuesOnly, keysOnly, flip

Create a generator that will only yield values, keys, or will flip them.

use Dakujem\Toru\Itera;

Itera::valuesOnly(iterable $input): iterable
Itera::keysOnly(iterable $input): iterable
Itera::flip(iterable $input): iterable

The flip function is similar to array_flip,
the valuesOnly function is similar to array_values,
and the keysOnly function is similar to array_keys.

use Dakujem\Toru\Itera;

Itera::valuesOnly(['a' => 'Adam', 'b' => 'Betty']); // ['Adam', 'Betty']
Itera::keysOnly(['a' => 'Adam', 'b' => 'Betty']);   // ['a', 'b']
Itera::flip(['a' => 'Adam', 'b' => 'Betty']);       // ['Adam' => 'a', 'Betty' => 'b']

Conversions: toArray, toArrayValues, toArrayMerge, toIterator, ensureTraversable

These functions immediately use the input.

Convert the input to array/Iterator from generic iterable.

use Dakujem\Toru\Itera;

Itera::toArray(iterable $input): array
Itera::toArrayMerge(iterable $input): array
Itera::toArrayValues(iterable $input): array
Itera::toIterator(iterable $input): \Iterator
Itera::ensureTraversable(iterable $input): \Traversable

💡

Iterators in general, Generators specifically, impose a challenge when being cast to arrays. Read the "Caveats" section below.

Itera::toArray(Itera::chain([1,2], [3,4])); // --> [3,4] ❗

There are 3 variants of the "to array" operation.

Toru function	Behaves like	Associative keys	Numeric keys	Values overwritten when keys overlap
toArray	array_replace	preserved	preserved	values with any overlapping keys ❗
toArrayMerge	array_merge	preserved	discarded	only values with associative keys
toArrayValues	array_values	discarded	discarded	no values are overwritten

Tapping: tap, each

Create a generator, that will call an effect function for each element upon iteration.

use Dakujem\Toru\Itera;

Itera::tap(iterable $input, callable $effect): iterable
Itera::each(iterable $input, callable $effect): iterable  // alias for `tap`

The signature of the effect function is

fn(mixed $value, mixed $key): void

The return values are discarded.

Repeating: repeat, loop, replicate

use Dakujem\Toru\Itera;

Itera::repeat(mixed $input): iterable
Itera::loop(iterable $input): iterable
Itera::replicate(iterable $input, int $times): iterable

The repeat function repeats the input as-is, indefinitely.
The loop function yields individual elements of the input, indefinitely.
The replicate function yields individual elements of the input, exactly specified number of times.

Both repeat and loop should be wrapped into a limit and valuesOnly if cast to arrays.

Please note that if the loop and replicate functions have a generator on the input, they may/will run into the issues native to generators - being non-rewindable and having overlapping indexes.

Producing: make, produce

The produce function will create an infinite generator that will call the provided producer function upon each iteration.

use Dakujem\Toru\Itera;

Itera::produce(callable $producer): iterable

It is supposed to be used with the limit function.

use Dakujem\Toru\Itera;

Itera::limit(Itera::produce(fn() => rand()), 1000); // a sequence of 1000 pseudorandom numbers
Itera::produce(fn() => 42); // an infinite sequence of the answer to life, the universe, and everything
Itera::produce(fn(int $i) => $i); // an infinite sequence of integers 0, 1, 2, 3, ...

The make function creates an iterable collection from its arguments. It is only useful in scenarios, where an iterator (a generator) is needed. Use arrays otherwise.

These two functions are only available as static Itera methods.

To produce both keys and values, one might use unfold to wrap the produce which would return key=>value pairs.

use Dakujem\Toru\Itera;

Itera::unfold(
    Itera::produce(fn(int $i) => [ calculateKey($i) => calculateValue($i) ])
);

Lazy evaluation

Generator functions are lazy by nature.
Invoking a generator function creates a generator object, but does not execute any code.
The code is executed once an iteration starts (e.g. via foreach).

By passing a generator as an input to another generator function, that generator is decorated and a new one is returned. This decoration is still lazy and no code execution occurs just yet.

use Dakujem\Toru\Dash;
use Dakujem\Toru\Itera;

// Create a generator from an input collection.
$collection = Itera::apply(input: Itera::filter(input: $input, filter: $filter), values: $mapper);
// or using Dash
$collection = Dash::collect($input)->filter(filter: $filter)->apply(values: $mapper);


// No generator code has been executed so far.
// The evaluation of $filter and $mapper callables begins with the first iteration below.
foreach($collection as $key => $value) {
    // Only at this point the mapper and filter functions are executed,
    // once per element of the input collection.
    // The generator execution is then _paused_ until the next iteration.
}

💡
If such an iteration was terminated before the whole collection had been iterated over (e.g. via break), the callables would NOT be called for the remaining elements.
This increases efficiency in cases, where it is unsure how many elements of a collection will actually be consumed.

Every function provided by Toru that returns iterable uses generators and is lazy.
Examples: adjust, map, chain, filter, flip, tap, slice, repeat

Other functions, usually returning mixed or scalar values, are aggregates and cause immediate iteration and generator code execution, exhausting generators on the input.
Examples: reduce, count, search, toArray, firstValue

Using keys (indexes)

Callable parameters of all the methods (mapper, predicate, reducer and effect functions) always receive keys along with values.

This is a key advantage over native functions like array_map, array_reduce or array_walk, even array_filter in its default setting.

Instead of

$mapper = fn($value, $key) => /* ... */;
$predicate = fn($value, $key): bool => /* ... */;

$collection = array_filter(array_map($mapper, $array, array_keys($array)), $predicate, ARRAY_FILTER_USE_BOTH);

it may be more convenient to

use Dakujem\Toru\Dash;

$mapper = fn($value, $key) => /* ... */;
$predicate = fn($value, $key): bool => /* ... */;

$collection = Dash::collect($array)->map($mapper)->filter($predicate);

With array_reduce this is even more convoluted, because there is no way to pass the keys to the native function.
One way to deal with it is to transform the array values to include the indexes and to alter the reducer to account for the changed data type.

$myActualReducer = fn($carry, $value, $key) => /**/;

// Transform the array into a form that includes keys
$transformedArray = array_map(function($key, $value) {
    return [$value, $key];
}, array_keys($array), $array);

// Apply array_reduce
$result = array_reduce($transformedArray, function($carry, array $valueAndKey) use ($myActualReducer){ 
    [$value, $key] = $valueAndKey;
    return $myActualReducer($carry, $value, $key);
});

Here, the solution may be even more concise

use Dakujem\Toru\Itera;

$myActualReducer = fn($carry, $value, $key) => /**/;

$result = Itera::reduce($array, $myActualReducer);

Custom transformations

To support custom transformation without interrupting a fluent call chain when using Dash, two methods are provided:

• Dash::alter
  • expects a decorator function returning an altered iterable collection
  • the iterable result is wrapped in a new Dash instance to continue the fluent call chain
• Dash::aggregate
  • expects an aggregate function that returns any value (mixed)
  • terminates the fluent chain

Dash::alter wraps the return value of the decorator into a new Dash instance, allowing for fluent follow-up.

use Dakujem\Toru\Dash;

Dash::collect(['zero', 'one', 'two', 'three',])
    ->alter(function (iterable $collection): iterable {
        foreach ($collection as $k => $v) {
            yield $k * 2 => $v . ' suffix';
        }
    })
    ->alter(function (iterable $collection): iterable {
        foreach ($collection as $k => $v) {
            yield $k + 1 => 'prefix ' . $v;
        }
    })
    ->filter( /* ... */ )
    ->map( /* ... */ );

Dash::aggregate returns any value produced by the callable parameter, without wrapping it into a new Dash instance.

Missing a "key sum" function? Need to compute the median value?

use Dakujem\Toru\Dash;
use Dakujem\Toru\Itera;

$keySum = Dash::collect($input)
    ->filter( /* ... */ )
    ->aggregate(function (iterable $collection): int {
        $keySum = 0;
        foreach ($collection as $k => $v) {
            $keySum += $k;
        }
        return $keySum;
    }); // no more fluent calls, integer is returned

$median = Dash::collect($input)
    ->filter( /* ... */ )
    ->aggregate(function (iterable $collection): int {
        return MyCalculus::computeMedian(Itera::toArray($collection));
    }); // the median value is returned

Extending Toru

Extending the Dash class may be considered to implement custom transformations or aggregations to use within the fluent call chain.
The Itera and IteraFn classes may be extended for consistence with extension to Dash.

use Dakujem\Toru\Dash;
use Dakujem\Toru\Itera;

class MyItera extends Itera
{
    /**
     * A shorthand for mapping arrays to use instead of `array_map`
     * with keys provided for the mapper.
     */
    public static function mapToArray(iterable $input, callable $mapper): iterable
    {
        return static::toArray(
            static::apply(input: $input, values: $mapper),
        );
    }

    public static function appendBar(iterable $input): iterable
    {
        return static::chain($input, ['bar' => 'bar']);
    }
}

class MyDash extends Dash
{
    public function appendFoo(): self
    {
        return new static(
            Itera::chain($this->collection, ['foo' => 'foo'])
        );
    }

    public function appendBar(): self
    {
        return new static(
            MyItera::appendBar($this->collection)
        );
    }

    public function aggregateZero(): int
    {
        return 0; // ¯\_(ツ)_/¯ 
    }
}

// 0 (zero)
MyDash::collect([1, 2, 3])->appendFoo()->appendBar()->aggregateZero();

// [1, 2, 3, 'foo' => 'foo', 'bar' => 'bar']
MyDash::collect([1, 2, 3])->appendFoo()->appendBar()->toArray();

// [1, 2, 3, 'foo' => 'foo', 'bar' => 'bar'] (generator)
MyItera::appendBar([1, 2, 3]);

Using a global alias

If you desire a global alias to create a Dash-wrapped collection, such as _dash, the best way is to register the global function in your bootstrap like so:

use Dakujem\Toru\Dash;

if (!function_exists('_dash')) {
    function _dash(iterable $input): Dash {
        return Dash::collect($input);
    }
}

You can also place this function definition inside a file (e.g. /bootstrap/dash.php) that you automatically load using Composer. In your composer.json file, add an autoloader rule as such:

{
  "autoload": {
    "files": [
      "bootstrap/dash.php"
    ]
  }
}

You no longer need to import the Dash class.

_dash($collection)->filter( /* ... */ )->map( /* ... */ )->toArray();

Take care when defining global function _ or __ as it may interfere with other functions (e.g. Gettext extension) or common i8n function alias.

Caveats

Generators, while being powerful, come with their own caveats:

1. working with keys (indexes) may be tricky
2. generators are not rewindable

Please understand generators before using Toru, it may help avoid a headache:
📖 Generators overview
📖 Generator syntax

Generators and caveats with keys when casting to array

There are two challenges native to generators when casting to arrays:

1. overlapping keys (indexes)
2. key types

Overlapping keys cause values to be overwritten when using iterator_to_array.
And since generators may yield keys of any type, using them as array keys may result in TypeError exception.

The combination of chain and toArray (or iterator_to_array) behaves like native array_replace:

use Dakujem\Toru\Itera;

Itera::toArray(
    Itera::chain([1, 2], [3, 4])
);

The result will be [3, 4], which might be unexpected. The reason is that the iterables (arrays in this case) have overlapping keys, and the later values overwrite the previous ones, when casting to array.

use Dakujem\Toru\Itera;

Itera::toArray(
    Itera::chain([
        0 => 1, 
        1 => 2,
    ], [
        0 => 3,
        1 => 4,
    ])
);

This issue is not present when looping through the iterator:

use Dakujem\Toru\Itera;

foreach(Itera::chain([1, 2], [3, 4]) as $key => $value){
    echo "$key: $value\n";
}

The above will correctly output

0:1
1:2
0:3
1:4

See this code in action: generator key collision

If we are able to discard the keys, then the fastest solution is to use toArrayValues, which is a shorthand for the chained call Itera::toArray(Itera::valuesOnly( $input )).

If we wanted to emulate the behaviour of array_merge, Toru provides toArrayMerge function.
This variant preserves the associative keys while discarding the numeric keys.

use Dakujem\Toru\Itera;

Itera::toArrayMerge(
    Itera::chain([
        0 => 1,
        1 => 2,
        'foo' => 'bar',
    ], [
        0 => 3,
        1 => 4,
    ])
);

That call will produce the following array:

[
     0 => 1,
     1 => 2,
     'foo' => 'bar',
     2 => 3,
     3 => 4,
]

💡

Note that generators may typically yield keys of any type, but when casting to arrays, only values usable as native array keys are permitted, for keys of other value types, a TypeError will be thrown.

Generators are not rewindable

Once an iteration of a generator is started, calling rewind on it will throw an error. This issue may be overcome using the provided Regenerator iterator (read below).

Supporting stuff

Regenerator

Regenerator is a transparent wrapper for callables returning iterators, especially generator objects. These may be directly generator functions, or callables wrapping them.

Regenerator enables rewinding of generators, which is not permitted in general. The generators are not actually rewound, but are created again upon each rewinding.

Since most of the iteration primitives in this library are implemented using generators, this might be handy.

Note: Rewinding happens automatically when iterating using foreach.

Let's illustrate it on an example.

$generatorFunction = function(): iterable {
    yield 1;
    yield 2;
    yield 'foo' => 'bar';
    yield 42;
};

$generatorObject = $generatorFunction();

foreach ($generatorObject as $key => $val) { /* ... */ }
// subsequent iteration will throw an exception
// Exception: Cannot rewind a generator that was already run
foreach ($generatorObject as $key => $val) { /* ... */ }

This may be solved by calling the generator function repeatedly for each iteration.

// Instead of iterating over the same generator object, the generator function
// is called multiple times. Each call creates a new generator object.
foreach ($generatorFunction() as $key => $val) { /* ... */ }
// A new generator object is created with every call to $generatorFunction().
foreach ($generatorFunction() as $key => $val) { /* ... */ } // ✅ no exception

In most cases, that will be the solution, but sometimes an iterable/Traversable object is needed.

use Dakujem\Toru\Dash;

// Not possible, the generator function is not iterable itself
$it = Dash::collect($generatorFunction);           // TypeError

// Not possible, the argument to `collect` must be iterable
$it = Dash::collect(fn() => $generatorFunction()); // TypeError

// The correct way is to wrap the generator returned by the call,
// but it has the same drawback as described above
$dash = Dash::collect($generatorFunction());       
foreach ($dash->filter($filterFn) as $val) { /* ... */ }
// Exception: Cannot rewind a generator that was already run
foreach ($dash->filter($otherFilterFn) as $val) { /* ... */ } // fails

This is where Regenerator comes into play.

use Dakujem\Toru\Dash;
use Dakujem\Toru\Regenerator;

$dash = new Regenerator(fn() => Dash::collect($generatorFunction()));
foreach ($dash->filter($filterFn) as $val) { /* ... */ }
foreach ($dash->filter($otherFilterFn) as $val) { /* ... */ } // works, hooray!

Regenerator internally calls the provider function whenever needed (i.e. whenever rewound), while also implementing the Traversable interface.

Storing intermediate value

Since most calls to Toru functions return generators, storing the intermediate value in a variable suffers the same issue.

use Dakujem\Toru\Itera;

$filtered = Itera::filter($input, $predicate);
$mapped = Itera::apply($filtered, $mapper);

foreach($mapped as $k => $v) { /* ...*/ }

// Exception: Cannot rewind a generator that was already run
foreach($filtered as $k => $v) { /* ...*/ }

Again, the solution might be to create a function, like this:

use Dakujem\Toru\Itera;

$filtered = fn() => Itera::filter($input, $predicate);
$mapped = fn() => Itera::apply($filtered(), $mapper);

foreach($mapped() as $k => $v) { /* ...*/ }

// this will work, the issue is mitigated by iterating over a new generator
foreach($filtered() as $k => $v) { /* ...*/ }

Alternatively, the Regenerator class comes handy.

use Dakujem\Toru\Itera;
use Dakujem\Toru\Regenerator;

$filtered = new Regenerator(fn() => Itera::filter($input, $predicate));
$mapped = new Regenerator(fn() => Itera::apply($filtered(), $mapper));

foreach($mapped as $k => $v) { /* ...*/ }

// In this case, the regenerator handles function calls.
foreach($filtered as $k => $v) { /* ...*/ }

Pipeline

A simple processing pipeline implementation. Useful with IteraFn class to compose processing algorithms.

use Dakujem\Toru\IteraFn;
use Dakujem\Toru\Pipeline;

$alteredCollection = Pipeline::through(
    $collection,
    IteraFn::filter(predicate: $filterFunction),
    IteraFn::map(values: $mapper),
);
// Pipelines are not limited to producing iterable collections, they may produce any value types:
$average = Pipeline::through(
    $collection,
    IteraFn::filter(predicate: $filterFunction),
    IteraFn::reduce(reducer: fn($carry, $current) => $carry + $current, initial: 0),
    fn(int $sum) => $sum / $sizeOfCollection,
);

Why iterables

Why bother with iterators when PHP has an extensive support for arrays?
There are many cases where iterators may be more efficient than arrays. Usually when dealing with large (or possibly even infinite) collections.

The use-case scenario for iterators is comparable to stream resources. You will know that stuffing uploaded files into a string variable is not the best idea all the time. It will surely work with small files, try that with 4K video, though.

A good example might be a directory iterator.
How many files might there be? Dozens? Millions? Stuffing that into an array may soon drain the memory reserves of your application.

So why use the iterable type hint instead of array?
Simply to extend the possible use-cases of a function/method, where possible.

Memory efficiency

The efficiency of generators stems from the fact that no extra memory needs to be allocated when doing stuff like chaining multiple collections, filtering, mapping and so on.

On the other hand, a foreach block will always execute faster, because there are no extra function calls involved. Depending on your use case, the performance difference may be negligible, though.

However, in cloud environments, memory may be expensive. It is a tradeoff.

In real-world scenarios, with OpCache enabled, using Toru would decrease memory usage with minimal/negligible impact on execution time.

For example, chaining multiple collections into one instead of using array_merge will be more efficient.

https://3v4l.org/Ymksm
https://3v4l.org/OmUb3
https://3v4l.org/HMasj

Also use comparison scripts in /tests/performance against your actual environment, if you are concerned about performance.

Alternatives

You might not need this library.

• mpetrovich/dash provides a full range of transformation functions, uses arrays internally
• lodash-php/lodash-php imitates Lodash and provides a full range of utilities, uses arrays internally
• nikic/iter implements a range of iteration primitives using generators, authored by a PHP core team member
• illuminate/collections should cover the needs of most Laravel developers, but uses arrays internally
• in many cases, a foreach will do the job

Toru library (dakujem/toru) does not provide a full range of ready-made transformation functions, rather provides the most common ones and means to bring in and compose own transformations.
It works well with and along with the aforementioned and other such libraries.

Toru originally started as an alternative to nikic/iter for daily tasks, which to me has a somewhat cumbersome interface.
The Itera static class tries to fix that by using a single class import instead of multiple function imports and by reordering the parameters so that the input collection is consistently the first one.
Still, composing multiple operations into one transformation felt cumbersome, so the IteraFn factory was implemented to fix that. It worked well, but was still kind of verbose for mundane tasks.
To allow concise fluent/chained calls (like with Lodash), the Dash class was then designed.
With it, it's possible to compose transformations neatly.

Contribution and future development

The intention is not to provide a plethora specific functions, rather offer tools for most used cases.

That being said, good quality PRs will be accepted.

Possible additions may include:

• combine values and keys
• zip multiple iterables (python, haskell, etc.)
• alternate multiple iterables (load-balance elements, mix)

---

Appendix: Example code with annotations

Illustration of various approaches

Observe the code below to see foreach and Dash solve a simple problem. See when and why Dash may be more appropriate than Itera alone.

use Dakujem\Toru\Itera;
use Dakujem\Toru\IteraFn;
use Dakujem\Toru\Pipeline;
use Dakujem\Toru\Dash;

$sequence = Itera::produce(fn() => rand()); // infinite iterator

// A naive foreach may be the best solution in certain cases...
$count = 0;
$array = [];
foreach ($sequence as $i) {
    if (0 == $i % 2) {
        $array[$i] = 'the value is ' . $i;
        if ($count >= 1000) {
            break;
        }
    }
}

// While the standalone static methods may be handy,
// they are not suited for complex computations.
$interim = Itera::filter($sequence, fn($i) => 0 == $i % 2);
$interim = Itera::reindex($interim, fn($i) => $i);
$interim = Itera::apply($interim, fn($i) => 'the value is ' . $i);
$interim = Itera::limit($interim, 1000);
$array = Itera::toArray($interim);

// Without the interim variable(s), the reading order of the calls is reversed
// and the whole computation is not exactly legible.
$array = Itera::toArray(
    Itera::limit(
        Itera::apply(
            Itera::reindex(
                Itera::filter(
                    $sequence,
                    fn($i) => 0 == $i % 2,
                ),
                fn($i) => $i,
            ),
            fn($i) => 'the value is ' . $i,
        ),
        1000,
    )
);

// Complex pipelines may be composed using partially applied callables.
$array = Pipeline::through(
    $sequence,
    IteraFn::filter(fn($i) => 0 == $i % 2),
    IteraFn::reindex(fn($i) => $i),
    IteraFn::apply(fn($i) => 'the value is ' . $i),
    IteraFn::limit(1000),
    IteraFn::toArray(),
);

// Lodash-style fluent call chaining.
$array = Dash::collect($sequence)
    ->filter(fn($i) => 0 == $i % 2)
    ->reindex(fn($i) => $i)
    ->map(fn($i) => 'the value is ' . $i)
    ->limit(1000)
    ->toArray();

Example: Listing images in a directory

Let us solve a simple task: List all images of a directory recursively.

You may have generative AI do this too, or come up with something like this:

$images = [];
$iterator = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($dir));
/** @var SplFileInfo $fileInfo */
foreach ($iterator as $fileInfo) {
    // Skip directories
    if ($fileInfo->isDir()) {
        continue;
    }
    // Get the full path of the file
    $filePath = $fileInfo->getPathname();
    // Reject non-image files (hacky)
    if (!@getimagesize($filePath)) {
        continue;
    }
    $images[$filePath] = $fileInfo;
}

This will work in development, but will have a huge impact on your server if you try to list millions of images, something not uncommon for mid-sized content-oriented projects.

The way to fix that is by utilizing a generator:

$listImages = function(string $dir): Generator {
    $iterator = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($dir));
    /** @var SplFileInfo $fileInfo */
    foreach ($iterator as $fileInfo) {
        // Skip directories
        if ($fileInfo->isDir()) {
            continue;
        }
        // Get the full path of the file
        $filePath = $fileInfo->getPathname();
        // Reject non-image files (hacky)
        if (!@getimagesize($fileInfo->getPathname())) {
            continue;
        }
        yield $filePath => $fileInfo;
    }
};
$images = $listImages($dir);

And what if you could create equivalent generator like this...

$images = _dash(new RecursiveIteratorIterator(new RecursiveDirectoryIterator($dir))) // recursively iterate over a dir
    ->filter(fn(SplFileInfo $fileInfo) => !$fileInfo->isDir())                       // reject directories
    ->filter(fn(SplFileInfo $fileInfo) => @getimagesize($fileInfo->getPathname()))   // accept only images (hacky)
    ->reindex(fn(SplFileInfo $fileInfo) => $fileInfo->getPathname());                // key by the full file path

It now depends on personal preference. Both will do the trick and be equally efficient.