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https://github.com/choonkeat/elm-auto-encoder-decoder
cli to watch *.elm file changes and generate Elm encoder and decoders for each type in the source code. used in https://github.com/choonkeat/elm-webapp
https://github.com/choonkeat/elm-auto-encoder-decoder
decoder elm encoder json
Last synced: 24 days ago
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cli to watch *.elm file changes and generate Elm encoder and decoders for each type in the source code. used in https://github.com/choonkeat/elm-webapp
- Host: GitHub
- URL: https://github.com/choonkeat/elm-auto-encoder-decoder
- Owner: choonkeat
- Created: 2019-12-16T15:38:27.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2024-06-16T10:20:29.000Z (7 months ago)
- Last Synced: 2024-12-16T16:14:47.430Z (26 days ago)
- Topics: decoder, elm, encoder, json
- Language: Elm
- Homepage: https://www.npmjs.com/package/elm-auto-encoder-decoder
- Size: 180 KB
- Stars: 8
- Watchers: 6
- Forks: 5
- Open Issues: 5
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# elm-auto-encoder-decoder
Generate automatic encoder and decoder. Leveraged by [choonkeat/elm-webapp](https://github.com/choonkeat/elm-webapp#readme) `Client` and `Server` instances to pass `Msg` to and fro.
_NOTE: While the generated decoders can always decode json encoded by the same version generator, there is no guarantee future versions can decode whatever was encoded in prior versions. :. If you're storing json for later retrieval, I do not recommend using the encoder/decoder here; I don't._
## Usage
```
npx elm-auto-encoder-decoder src/Types.elm
```
any time `src/Types.elm` file changes, `src/Types/Auto.elm` will be regenerated.
## ENV variable configurations
`GENERATED_SRC` will write `Auto.elm` files to a different directory than the source files, while keeping the directory hierarchy. e.g. `GENERATED_SRC=generated/src`
`WATCHING` when set to `false` will exit after a single run, instead of hanging around waiting for file changes. e.g. `WATCHING=false`
`EXTRA_IMPORT` is written to all `Auto.elm` files if present, e.g. `EXTRA_IMPORT='Time.Extra excposing (..)'`
## How it works
An Elm module `Foo.Bar` like below
``` elm
module Foo.Bar exposing (..)
type alias Choice =
Option Bool
type Option a
= None
| Some a
```
will be encoded and decoded as JSON like
```json
["Foo.Bar.None"]
["Foo.Bar.Some",true]
```
by the generated Elm functions in the corresponding [`Foo.Bar.Auto` module function](https://github.com/choonkeat/elm-auto-encoder-decoder/blob/21a3cd4d46e8bbdd418a3069fb5b79f6efd6a1be/src/Foo/Bar/Auto.elm#L242-L246)
### Auto encoder decoders of related types
If `src/A.elm` imports from `src/B.elm`, its better to provide both filenames to the cli. The generated encoder/decoder of `A` will automatically reference the generated encoder/decoder of `B`
### Exposed types
No encoder/decoder functions will be generated for types that are not fully exposed. i.e. a custom type has to be exposed with `(..)` e.g. `MyType(..)`.
However, if there are exposed types that are composed from unexposed types, you're expected to supply the encoder/decoder functions manually by naming convention (see next point)
### Don't be alarmed with "I cannot find ... variable" compiler errors
If your `src/Types.elm` contain types imported from other modules, e.g. `Time.Posix`
```elm
type alias User = { name : String, createdAt : Time.Posix }
```
the generated code will likely not compile
```
-- NAMING ERROR --------------------------------------------- src/Types/Auto.elm
I cannot find a `decodeTimePosix` variable:
248| |> Json.Decode.map2 (|>) (Json.Decode.at [ "createdAt" ] (decodeTimePosix))
^^^^^^^^^^^^^^^
-- NAMING ERROR --------------------------------------------- src/Types/Auto.elm
I cannot find a `encodeTimePosix` variable:
197| , ("createdAt", (encodeTimePosix) value.createdAt)
^^^^^^^^^^^^^^^
```
**just implement and expose those function names** in your source `src/Types.elm` (or a different file specified by `EXTRA_IMPORT` env), for example:
``` elm
decodeTimePosix : Json.Decode.Decoder Time.Posix
decodeTimePosix =
Json.Decode.int
|> Json.Decode.map Time.millisToPosix
encodeTimePosix : Time.Posix -> Json.Encode.Value
encodeTimePosix t =
Json.Encode.int (Time.posixToMillis t)
```