View Source Credo.Check.Refactor.DoubleBooleanNegation (Credo v1.7.7-rc.0)
Basics
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.credo.exs
.
This check is tagged
:controversial
This means that this check is more opinionated than others and not for everyone's taste.
This check has a base priority of low
and works with any version of Elixir.
Explanation
Having double negations in your code can obscure the parameter's original value.
# NOT preferred
!!var
This will return false
for false
and nil
, and true
for anything else.
At first this seems like an extra clever shorthand to cast anything truthy to
true
and anything non-truthy to false
. But in most scenarios you want to
be explicit about your input parameters (because it is easier to reason about
edge-cases, code-paths and tests).
Also: nil
and false
do mean two different things.
A scenario where you want this kind of flexibility, however, is parsing
external data, e.g. a third party JSON-API where a value is sometimes null
and sometimes false
and you want to normalize that before handing it down
in your program.
In these case, you would be better off making the cast explicit by introducing a helper function:
# preferred
defp present?(nil), do: false
defp present?(false), do: false
defp present?(_), do: true
This makes your code more explicit than relying on the implications of !!
.
Check-Specific Parameters
There are no specific parameters for this check.
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