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Add more docs about :optional in Inspect #14399

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Apr 5, 2025
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Add more docs about :optional in Inspect #14399

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17 changes: 13 additions & 4 deletions lib/elixir/lib/inspect.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -64,9 +64,10 @@ defprotocol Inspect do

* `:except` - remove the given fields when inspecting.

* `:optional` - (since v1.14.0) do not include a field if it
matches its default value. This can be used to simplify the
struct representation at the cost of hiding information.
* `:optional` - (since v1.14.0) a list of fields that should not be
included when they match their default value. This can be used to
simplify the struct representation at the cost of hiding
information.

Whenever `:only` or `:except` are used to restrict fields,
the struct will be printed using the `#User<...>` notation,
Expand All @@ -82,7 +83,15 @@ defprotocol Inspect do
#=> #User<id: 1, name: "Jane", ...>

If you use only the `:optional` option, the struct will still be
printed as `%User{...}`.
printed as a valid struct.

defmodule Point do
@derive {Inspect, optional: [:z]}
defstruct [x: 0, y: 0, z: 0]
end

inspect(%Point{x: 1})
%Point{x: 1, y: 0}

## Custom implementation

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