module ActiveSupport::Deprecation::Behavior

Returns the current behavior or if one isn't set, defaults to +:stderr+.

def behavior
  @behavior ||= [DEFAULT_BEHAVIORS[:stderr]]
end

}
# custom stuff
ActiveSupport::Deprecation.behavior = ->(message, callstack) {
ActiveSupport::Deprecation.behavior = MyCustomHandler
ActiveSupport::Deprecation.behavior = [:stderr, :log]
ActiveSupport::Deprecation.behavior = :stderr

because they happen before Rails boots up.
Deprecation warnings raised by gems are not affected by this setting
Setting behaviors only affects deprecations that happen after boot time.

[+silence+] Do nothing.
[+notify+] Use +ActiveSupport::Notifications+ to notify +deprecation.rails+.
[+log+] Log all deprecation warnings to +Rails.logger+.
[+stderr+] Log all deprecation warnings to +$stderr+.
[+raise+] Raise ActiveSupport::DeprecationException.

Available behaviors:

or an object that responds to +call+.
Sets the behavior to the specified value. Can be a single value, array,

def behavior=(behavior)
  @behavior = Array(behavior).map { |b| DEFAULT_BEHAVIORS[b] || b }
end