A field with a default value set to nil should not be enforced

[lasseebert]

When the struct has enforce: true, one can override this by setting a default value on a field. Something like this:

typedstruct enforce: true do
  field :non_enforced_field, integer, default: 42
end

But it is not possible to default to nil (it will not un-enforce the field:

typedstruct enforce: true do
  # This will not work. The field is still enforced
  field :non_enforced_field, integer | nil, default: nil
end

I know that adding enforce: false on the field will do the same thing, since nil is the default value for non-enforces fields, but for the explicitness and readability, it would be nice the set the default value to nil.

If you agree, @ejpcmac, I will be happy to give it a shot.

[ejpcmac]

Hello @lasseebert,

An enforced value must be non-nil. By setting enforce: true globally, you mean that :non_enforced_field is in fact enforced. The way you define it says the same thing as doing:

defmodule Test do
  @enforce_keys [:non_enforced_field]
  defstruct non_enforced_field: nil

  @type t() :: %__MODULE__{non_enforced_field: integer() | nil}
end

Which is obviously invalid: you cannot create a %Test{} with :non_enforced_field set to nil.

In your first example, the enforce: true is not overriden: the field is still enforced, but since it has a default value, your user do not need to provide a non-nil value.

[lasseebert]

@ejpcmac

Thanks for the explanation :)
I thought setting a default value would unset the global enforce: true for that field (ref the docs):

A key with a default value is not enforced.

which is why I expected

typedstruct enforce: true do
  field :non_enforced_field, integer | nil, default: nil
end

to generate something like

defmodule Test do
  @enforce_keys []
  defstruct non_enforced_field: nil

  @type t() :: %__MODULE__{non_enforced_field: integer() | nil}
end

[ejpcmac]

I thought setting a default value would unset the global enforce: true for that field (ref the docs):

A key with a default value is not enforced.

Mmm. Maybe that’s a documentation issue then. I’ll fix it in the next release.

[lasseebert]

Thanks for your quick responses. It all makes sense :)
I will consider this issue closed, but I will let you close it in case you want to leave it open for the doc changes.

[ejpcmac]

@lasseebert You’re welcome. Please let it open so I can remember it.

[ejpcmac]

Mmm. In fact that’s a bug. Reading my tests, I have :

test "does not enforce keys for fields with a default value" do
  refute :with_default in EnforcedTypedStruct.enforce_keys()
end

test "does not enforce keys for fields with a default value set to `false`" do
  refute :with_false_default in EnforcedTypedStruct.enforce_keys()
end

So I’ll add a test for the default value set to nil. That’s a corner case. Property testing would have catch it, but I haven’t got the time to figure how to property-test code generation.

[lasseebert]

Awesome 👍 🙂