toraritte
What is the specific syntax of @derive module attribute and where is it documented explicitly?
Hi,
(I also asked on Stackoverflow, I hope cross-posting is ok.)
I expected it to be documented in Module, probably with references to structs, but no joy. Seen it used with a single or a list of arguments. All the variations I could find so far:
-
list of module names such as
@derive [MyProtocol, Another](e.g.,
Kernel.defstruct/1macro doc,
line 65 inProtocolTest(v1.7.4)) -
module name such as
@derive Inspect -
tuple in the form of
@derive {Protocol, key1: :val1, :others}(e.g., line 550 in
InspectTest(v1.8.0-rc.0),
Phoenix.Paramprotocol doc) -
list of tuples such as
@derive [{Prot1, :options}, {Prot2, key: :val}]
The only places I found mentions of @derive:
- “Deriving” section in the documentation of
Kernel.defstruct/1macro - New (i.e., v1.8.0-rc.0) “Deriving” section of
Inspect - Documentation of
Protocol.derive/3macro (added in #7019)
(This was extremely helpful because using the example snippets one can test all the combinations above.)
Wasn’t sure whether I’m not just overlooking something, therefore didn’t open an issue or pull request.
Marked As Solved
kip
This has bugged me for a while too. The docs @NobbZ pointed to say:
Yet there are non-confirming examples that clearly work but aren’t documented anywhere I can see either. Like in Poison:
defmodule PersonOnlyName do
@derive {Poison.Encoder, only: [:name]}
defstruct [:name, :age]
end
defmodule PersonWithoutName do
@derive {Poison.Encoder, except: [:name]}
defstruct [:name, :age]
end
Clearly not a list of modules either! The docs for Protocol give some clarity to what is actually going on under the hood.
And indeed, for Poison, the implementation follows this mechanism.
I think this is one part of the docs that could be improved (I wonder if its on @eksperimental’s list of planned improvements).
Also Liked
NobbZ
Its documented in Kernel.defstruct/1.
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