Twig Lambda

Lambda expressions for Twig and filters that make use of them

---

Quick examples

Listing names of all authors ordered by age:

{% for author in articles|map(=> _.author)|unique_by('===')|sort_by(=> _.age) %}
    * {{ author.name }}, {{ author.age }}
{% endfor %}

Counting elements starting from specified letter:

{% for key, count in ['foo', 'bar', 'foobar']|countBy(=> _|first|capitalize) %}
    * {{ count }} elements start from {{ key }}.
{% endfor %}

---

Installation

Install via Composer:

composer require dpolac/twig-lambda

Add the extension to Twig:

$twig->addExtension(new \DPolac\TwigLambda\LambdaExtension());

... or if you use Symfony, add the following to your services.yml config file:

services:
    # ...
    dpolac.twig_lambda.extension:
        class: DPolac\TwigLambda\LambdaExtension
        tags: [ { name: twig.extension } ]

---

Usage

Lambda expression

To create lambda expression prepend any valid Twig expression with => operator. Inside of the lambda expression you can use any variable from the outside. There are also two special variables available:

• _ (single underscore) - first argument,
• __ (double underscore) - array of arguments counted from zero.

=> _.name
=> _ * 2
=> _|first
=> 'foobar'
=> _ is even
=> __[0] + __[1]

To create lambda expression with list of arguments, add it before => operator. Separate multiple arguments with semicolons. You can use brackets for readability.

x => x + 1
(book) => book.author
arg1; arg2 => arg1 ~ arg2
(a; b; c) => a + b - c

Note that if you use list of arguments, _ variable is not longer available.

---

Below is a list of available filters and tests. All works with arrays and any Traversable object and preserve it keys. All lambdas are called with two arguments: element and key.

---

|map

Alias: |select
Signature: array|map(lambda)

Applies a given function to each element and returns array of results in the same order.

{% for i in  [1, 2, 3, 4]|map(=> _ * 2) %}
    {{ i }} {# prints '2 4 6 8' #}
{% endfor %}

---

|filter

Alias: |where
Signature: array|filter(lambda)

Returns array of elements that passes a test specified by lambda.

{% for i in [1, 2, 3, 4, 5, 6]|filter(=> _ is even) %}
    {{ i }} {# prints '2 4 6' #}
{% endfor %}

---

|unique_by

Signature: array|unique_by(lambda|'==='|'==')

Returns array of unique elements. Uniqueness is checked with passed lambda. PHP operators == or === will be used if string '==' or '===' is passed instead of lambda.

Lambda should have two arguments - items to check. Keys of elements are also passed as third and fourth argument.

    {% for i in [1, 2, 2, 3, 1]|unique_by((i1;i2) => i1 == i2) %}
        {{ i }} {# prints '1 2 3' #}
    {% endfor %}

equivalent

    {% for i in [1, 2, 2, 3, 1]|unique_by('==') %}
        {{ i }} {# prints '1 2 3' #}
    {% endfor %}

---

|group_by

Signature: array|group_by(lambda)

Sorts an array into groups by the result of lambda.

{% for key, group in ['foo', 'bar', 'foobar', 'barbar']|group_by(=> _|first|capitalize) %}
    = {{ key }}
    {% for i in group %}
        * {{ i }}
    {% endfor %}
{% endfor %}

will produce

    = F
        * foo
        * foobar
    = B
        * bar
        * barbar

---

|sort_by

Signature: array|sort_by(lambda[, direction = 'ASC'])

Sorts array by values returned by lambda. Direction can be 'ASC' or 'DESC'.

{% for i in ['bar', 'fo', 'foobar', 'foob']|sort_by(=> _|length, 'DESC') %}
    {{ i }} {# prints 'foobar foob bar fo' #}
{% endfor %}

---

|count_by

Signature: array|count_by(lambda)

Sorts an array into groups and returns a count for the number of objects in each group.

If lambda returns true, false or null, it will be converted to string 'true', 'false' or 'null'. Float will be converted to integer.

{% for key, count in ['foo', 'bar', 'foobar']|count_by(=> _|first|capitalize) %}
    * {{ count }} elements start from {{ key }}.
{% endfor %}

will produce

    * 2 elements start from F
    * 1 elements start from B

---

is any

Signature: array is any(lambda)

Returns true if lambda returns true for any element from an array.

Returns false if array is empty.

{{ [1, 2, 3] is any(=> _ is even) ? "There is even element in the array." }}
{# prints 'There is even element in the array.' #}

---

is every

Signature: array is every(lambda)

Returns true if lambda returns true for every element from an array.

Returns true if array is empty.

{{ [1, 2, 3] is every(=> _ > 0) ? "All elements in the array are positive." }}
{# prints 'All elements in the array are positive.' #}

---

call()

Signature: call(lambda [, arguments:array])

Calls lambda and returns its result. You can provide array of arguments.

This function is provided to allow creating twig macros taking lambda as an argument.

{{ call(=> _ * 2, [10]) }}
{# prints '20' #}
{{ call(=> _.foo, [{foo: 12}]) }}
{# prints '12' #}