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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')>>