Nim Json

json_examples.nim

import json
import marshal
import options

type
    Message = object
        id: int
        message: string
    OptionalMessage = object
        id: int
        message: Option[string]
    
var message = Message(message: "Hello", id: 1)

echo $$message # Marshal can just serialize a type to JSON
# -> {"id": 1, "message": "Hello"}

var messages = @[message]

echo $$messages
# -> [{"id": 1, "message": "Hello"}]

var optMessage = OptionalMessage(id: 1, message: some("hello"))

echo $$optMessage
# -> {"id": 1, "message": {"val": "hello", "has": true}}

converter toMessage(message: OptionalMessage): Message =
    result = Message(id: message.id, message: get(message.message, ""))

echo $$toMessage(optMessage)
# -> {"id": 1, "message": "hello"}

try:
    # will raise the first key error it finds in the order 
    # of declared object properties but not others
    echo $to(parseJson("""{ "bobo": "chimp" }"""), Message)
except:
    echo getCurrentExceptionMsg()

try:
    # will still raise id error
    echo $to(parseJson("""{ "message": "chimp" }"""), Message)
except:
    echo getCurrentExceptionMsg()
    # key not found: id

try:
    echo $to(parseJson("""{ "id": "chimp" }"""), Message)
except:
    echo getCurrentExceptionMsg()
    # key not found: id

echo $to(parseJson("""{ "id": 1 }"""), OptionalMessage)
# -> OptionalMessage(id: 1, message: None[string])