scala - Spray Json `RootJsonFormat`'s Invariance? -

-

given following:

scala> trait parent defined trait parent  scala> case class boy(name: string) extends parent defined class boy  scala> case class girl(id: int) extends parent defined class girl

i tried define implicit formatter (de-serialization , serialization) them:

scala> object formats extends defaultjsonprotocol {       |   implicit val format: rootjsonformat[parent] = jsonformat1(boy.apply)      |   implicit val girlformat: rootjsonformat[parent] = jsonformat1(girl.apply)      | }

but got compile-time errors:

<console>:22: error: type mismatch;  found   : spray.json.rootjsonformat[boy]  required: spray.json.rootjsonformat[parent] note: boy <: parent, trait rootjsonformat invariant in type t. may wish define t +t instead. (sls 4.5)          implicit val format: rootjsonformat[parent] = jsonformat1(boy.apply)                                                                   ^ <console>:23: error: type mismatch;  found   : spray.json.rootjsonformat[girl]  required: spray.json.rootjsonformat[parent] note: girl <: parent, trait rootjsonformat invariant in type t. may wish define t +t instead. (sls 4.5)          implicit val girlformat: rootjsonformat[parent] = jsonformat1(girl.apply)                                                                       ^

as understand compile-time error message, rootjsonformat invariant type parameter.

why that?


Comments

Post a Comment

Popular posts from this blog

python - No exponential form of the z-axis in matplotlib-3D-plots -

-
Image
i have similar problem described in how prevent numbers being changed exponential form in python matplotlib figure : i don't want (in special case) weird scientific formatting of axis. problem different have problem @ z -axis. 2-d plots can use ax.get_yaxis().get_major_formatter().set_useoffset(false) . , there no function ax.get_zaxis() what use format z -axis same way? edit: example: from mpl_toolkits.mplot3d import axes3d import numpy np import sys import matplotlib import matplotlib.pyplot pyplot def func(xi, ti): res = 10e3 + np.cos(ti) * np.sin(xi) return res if __name__ == '__main__': timespacing = 20 timestart = 0 timeend = 1 time = np.linspace(timestart, timeend, timespacing) widthspacing = 50 widthstart = 0 widthend = 3 width = np.linspace(widthstart, widthend, widthspacing) reslist = [] matplotlib.rcparams['legend.fontsize'] = 10 fig = pyplot.figure() ax = fig.gca(projection = '3d...
Read more

php - Best Light server (Linux + Web server + Database) for Raspberry Pi -

-
i install web server database on raspberry pi (little computer). computer has 1gb ram. i want know best combination: linux distribution , web server , dbms run local server multiple users minimal latency, use php on server. , best settings performance , not have bugs (memory usage, disable plugin, disable service, etc)? i thought light debian , lighttpd server , sqlite database. solution? i think lighttpd + sqlite great choice. linux distro, debian @ centos or tiny core linux , although i'm not sure of compatibility pi. obviously, can't go wrong raspbian if want use in production , more stable performance, few more pi's , set them in cluster .
Read more

c# - "Newtonsoft.Json.JsonSerializationException unable to find constructor to use for types" error when deserializing class -

-
i developing app in xamarin android. have splash screen serialize class , pass mainactivity using intent . when try deserialize in mainactivity error message : "serializationexception unable find constructor use types" serialization : void loaddata() { currency currency = new currency(this); intent = new intent(this, typeof(mainactivity)); intent.putextra("currency", newtonsoft.json.jsonconvert.serializeobject(currency)); startactivity(intent); } deserialization : cur = newtonsoft.json.jsonconvert.deserializeobject<currency> (intent.getstringextra("currency")); // error here class constructor : public currency(context context) { thiscontext = context; } i began experiencing problem after added parameter context context constructor. has caused this? how can solve it? possible serialize/deserialize class has parameters? you need have empty constructor in currency class in order deserialize it. ...
Read more