Experimental Features

The following pages of documentation describe Hack language features in the experimental phase.

About Experimental Features

We have documented these features as they may appear in built-ins, including the Hack Standard Library.

We do not recommend using any of these features until they are formally announced and integrated into the main documentation set.

Enabling an Experimental Feature

To use an experimental feature, add the __EnableUnstableFeatures file attribute to any files containing that feature.

<<file:__EnableUnstableFeatures('experimental_feature_name')>>

You can also specify multiple features:

<<file:__EnableUnstableFeatures('experimental_feature_name', 'other_experimental_feature_name')>>