如何派生Data.Messagepack 1.0.0的实例 [英] How to derive instances of Data.Messagepack 1.0.0

问题描述

以前版本的 Data.Messagepack ， 0.7.2.5 支持通过模板Haskell导出实例。但是，当前版本（1.0.0）不。 p>

因此，我想知道是否有另一种方法来自动派生MessagePack 1.0.0实例，可能使用 XDeriveGeneric ？

解决方案

作为权宜之计，看看 msgpack-aeson 消息包的目录 github repo：

https://github.com/msgpack/msgpack-haskell/tree/master/msgpack-aeson

你可以从你的数据值 - > aeson < - >消息包。不一定高效，但方便，因为您可以通过 DeriveGeneric 自动获取ToJSON和FromJSON。

示例代码： p>

  { - ＃LANGUAGE DeriveGeneric，OverloadedStrings＃ - } 
 
导入Data.MessagePack.Aeson 
将合格的Data.MessagePack导入为MP 
 import GHC.Generics 
 import Data.Aeson 
 
 data Foo = Foo {_a :: Int，_b :: String} 
派生（通用）
 
实例ToJSON Foo 
实例FromJSON Foo 
 
 toMsgPack :: Foo  - >也许MP.Object 
 toMsgPack = decode。编码
 
 test = toMsgPack（Foo 3asd）
  

The previous version of Data.Messagepack, 0.7.2.5 supports deriving instances via Template Haskell. The current version (1.0.0), however, doesn't.

I was hence wondering if there is an alternative way to automatically derive MessagePack 1.0.0 instances, possibly using XDeriveGeneric?

解决方案

As a stop-gap measure, have a look at the msgpack-aeson directory of the message-pack github repo:

https://github.com/msgpack/msgpack-haskell/tree/master/msgpack-aeson

You could go from your data values <-> aeson <-> message-pack. Not necessarily efficient, but convenient since you can auto derive ToJSON and FromJSON with DeriveGeneric.

Example code:

{-# LANGUAGE DeriveGeneric, OverloadedStrings #-}

import Data.MessagePack.Aeson
import qualified Data.MessagePack as MP
import GHC.Generics
import Data.Aeson

data Foo = Foo { _a :: Int, _b :: String }
  deriving (Generic)

instance ToJSON Foo
instance FromJSON Foo

toMsgPack :: Foo  -> Maybe MP.Object
toMsgPack =   decode . encode

test = toMsgPack (Foo 3 "asd")

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