Fix example in Hash#from

[wooster0]

This is the current code:

require "json"

def speak_about(thing : String, n : Int64)
  "I see #{n} #{thing}s"
end

data = JSON.parse(%({"thing": "world", "n": 2})).as_h
speak_about(**{thing: String, n: Int64}.from(data)) # => "I see 2 worlds"

which results in:

Error in line 8: instantiating 'NamedTuple(thing: String.class, n: Int64.class)#from(Hash(String, JSON::Any))'

in /usr/lib/crystal/named_tuple.cr:77: expanding macro

    {% begin %}
    ^

in macro 'macro_94851401795888' /usr/lib/crystal/named_tuple.cr:77, line 4:

   1. 
   2.       NamedTuple.new(
   3.       
>  4.         "thing": self[:thing].cast(hash.fetch(:thing) { hash["thing"] }),
   5.       
   6.         "n": self[:n].cast(hash.fetch(:n) { hash["n"] }),
   7.       
   8.       )
   9.     

instantiating 'String.class#cast(JSON::Any)'
in /usr/lib/crystal/class.cr:124: can't cast JSON::Any to String

    other.as(self)
    ^

Because every value of data is JSON::Any.

Now it's:

require "json"

def speak_about(thing : String, n : Int64)
  "I see #{n} #{thing}s"
end

hash = JSON.parse(%({"thing": "world", "n": 2})).as_h

# Cast types appropriately:
data = {} of String => JSON::Any::Type
hash.each { |key, value| data[key] = value.raw }

speak_about(**{thing: String, n: Int64}.from(data)) # => "I see 2 worlds"

which appropriately casts every value to the real, raw type.

[bcardiff]

Maybe having the following shorter snippet with type annotation might be useful for the user.

hash = JSON.parse(%({"thing": "world", "n": 2})).as_h # hash : Hash(String, JSON::Any)
data = hash.transform_values(&.raw)                   # data : Hash(String, String | Int64 | Array(JSON::Any) | ... )
speak_about(**{thing: String, n: Int64}.from(data))   # => "I see 2 worlds"

[bcardiff]

The word appropriately might not be clear for the future reader. Showing the evolution of types would be more straight.

[asterite]

I have no idea how this works:

{thing: String, n: Int64}.from(data)

It should be:

NamedTuple(thing: String, n: Int64).from(data)

[asterite]

Oh, nevermind... it's a bit hacky, but well...