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# erl_features (stdlib v7.3)

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This module contains functions for supporting features that can be enabled/disabled in Erlang.

It should be considered as mostly for internal use, although there are some functions that might be useful when writing tools.

## Summary

### Types

feature()
release()
status()
type()

### Functions

all()

Return a list of all known features. This list will include features that have been removed (status `rejected`) and features that are no longer configurable (status `permanent`).

configurable()

Return a list of all configurable features, that is, features with status `experimental` or `approved`. These are the features that can be enabled or disabled.

enabled()

Return a list of the features that are currently enabled. Note that the set of enabled is set during startup and can then not be changed.

info(Feature)

Return a map containing information about the given feature.

used/1

Return the list of features enabled when compiling the module. The module need not be loaded, but is found if it exists in the loadpath. If not all features used by the module are enabled in the runtime, loading the module is not allowed.

## Types

# feature()

(not exported) (since OTP 25.0)

    -type feature() :: atom().

# release()

(not exported) (since OTP 25.0)

    -type release() :: non_neg_integer().

# status()

(not exported) (since OTP 25.0)

    -type status() :: experimental | approved | permanent | rejected.

# type()

(not exported) (since OTP 25.0)

    -type type() :: extension | backwards_incompatible_change.

## Functions

# all()

(since OTP 25.0)

    -spec all() -> [feature()].

Return a list of all known features. This list will include features that have been removed (status `rejected`) and features that are no longer configurable (status `permanent`).

# configurable()

(since OTP 25.1)

    -spec configurable() -> [feature()].

Return a list of all configurable features, that is, features with status `experimental` or `approved`. These are the features that can be enabled or disabled.

# enabled()

(since OTP 25.0)

    -spec enabled() -> [feature()].

Return a list of the features that are currently enabled. Note that the set of enabled is set during startup and can then not be changed.

# info(Feature)

(since OTP 25.0)

    -spec info(feature()) -> FeatureInfoMap | no_return()
                  when
                      Description :: string(),
                      FeatureInfoMap ::
                          #{description := Description,
                            short := Description,
                            type := type(),
                            keywords := [atom()],
                            status := status(),
                            experimental => release(),
                            approved => release(),
                            permanent => release(),
                            rejected => release()}.

Return a map containing information about the given feature.

# used/1

(since OTP 25.0)

    -spec used(module() | file:filename()) -> [feature()].

Return the list of features enabled when compiling the module. The module need not be loaded, but is found if it exists in the loadpath. If not all features used by the module are enabled in the runtime, loading the module is not allowed.