Creating a custom Twig filter

Similar to a Twig function used to extract or generate content, a Twig filter can be used to transform a value into something different.

We can use the same WeatherExtension class that we used before to add our custom functions, but this time we’ll implement the getFilters() method:

public function getFilters(): array {
  return [
    new TwigFilter(
      'celsius_to_fahrenheit',
      [$this, 'celsiusToFahrenheit']
    ),
  ];
}

Staying in the field of meteorology, we’ve implemented a Twig filter to convert a temperature value from Celsius to Fahrenheit. The code for the filter is a simple one-line method:

public function celsiusToFahrenheit(
  float $celsius
): float {
  return $celsius * 1.8 + 32;
}

WeatherExtension is already tagged to be a Twig extension (in the...