Reading a JSON file

---

examples/json/math.json

{
    "status": 200,
    "status_text": "OK",
    "count": 3,
    "otzzz": 23,
    "results": [
        {
            "name": "pi",
            "value": 3.14
        },
        {
            "name": "e",
            "value": 2.71
        },
        {
            "name": "Square root of 2",
            "value": 1.41
        }
    ]
}

examples/json/read_math_json.cr

require "json"

alias Constant = NamedTuple(name: String, value: Float64)
alias MathResponseType = NamedTuple(
  status: Int32,
  status_text: String,
  count: Int32,
  results: Array(Constant))
main

def main
  if ARGV.size != 1
    puts "Needs filename eg. math.json"
    exit 1
  end
  filename = ARGV[0]
  content = File.read(filename)
  data = MathResponseType.from_json(content)
  puts data
  puts data["results"][0].keys
end

# This will complain if field is missing or the value of a field is of incorrect type,
# but it will silently ignore any extra fields