Pluggable/composable coercion upcoming in RSchema v3

rschema_pluggable_coercion.rb

# params usually come in as strings, regardless of the actual type they are
params = {
  'fruit' => 'banana',
  'harvested_at' => '2017-05-08T01:46:16+10:00',
  'unwanted_framework_crap' => 'DHH',
}

# you can declare what the types are _supposed_ to be with a schema
schema = RSchema.define {{
  fruit: _Symbol,
  harvested_at: _Time,
  is_ripe: Boolean(),
}}

# but schemas are strict by default, and will not accept the param strings
result = schema.call(params)
puts result.valid? #=> false

# so, to enable coercion, you can wrap coercers around the schema
coercing_schema = RSchema::RACK_PARAM_COERCER.wrap(schema)

# this new schema will coerce and accept the params
result = coercing_schema.call(params)
result.valid? #=> true
result.value #=>
#  {
#    :fruit => :banana,
#    :harvested_at => #<Time 2017-05-08 01:46:16 +1000>,
#    :is_ripe => false,
#  }


# These coercion wrappers are composed of many small coercers,
# which gives fine-grained control over what does/doesn't get
# coerced.
module RSchema
  RACK_PARAM_COERCER = CoercionWrapper.new do
    coerce_type Symbol, with: Coercers::Symbol
    coerce_type Integer, with: Coercers::Integer
    coerce_type Float, with: Coercers::Float
    coerce_type Time, with: Coercers::Time
    coerce_type Date, with: Coercers::Date

    coerce Schemas::Boolean, with: Coercers::Boolean
    coerce Schemas::FixedHash, with: [
      Coercers::FixedHash::SymbolizeKeys,
      Coercers::FixedHash::RemoveExtraneousAttributes,
      Coercers::FixedHash::DefaultBooleansToFalse,
    ]
  end
end