Custom types can set a message to be used in the response when invalid

[dnesteryuk]

Just return an instance of Grape::Types::InvalidValue with the message:

class Color
  def self.parse(value)
    return value if %w[blue red green].include?(value)

    Grape::Types::InvalidValue.new('Invalid color')
  end
end

Any raised exception will be treated as an invalid value as it was before.

Implements an idea listed in #2093

[dblock]

This is great, but I think we should rely on an exception to separate valid returns from errors in the flow. We could similarly rescue StandardError and convert it into something with more detail like a ParseError that would help the caller identify the actual parameter that could not be parsed. WDYT?

[dblock]

I feel like this should be a raise that gets handled, not a return.

[dnesteryuk]

How will we know that an exception message should be returned to the user if we rescue StandardError? I would like to avoid guessing 🙂 We already return the invalid value there and there and there.

In general, if there is an easy way to return a value indicating a failure, I prefer to do that. It is cheaper:

require 'benchmark/ips'

def return_value
  :invalid
end

def raise_exception
  raise StandardError
end

Benchmark.ips do |x|
  x.report('return value') do
    return_value
  end
  x.report('raise error') do
    begin
      raise_exception
    rescue StandardError
    end
  end

  x.compare!
end

Warming up --------------------------------------
        return value     1.990M i/100ms
         raise error   149.703k i/100ms
Calculating -------------------------------------
        return value     19.948M (± 0.4%) i/s -    101.470M in   5.086841s
         raise error      1.513M (± 0.5%) i/s -      7.635M in   5.044907s

Comparison:
        return value: 19947800.7 i/s
         raise error:  1513417.9 i/s - 13.18x  (± 0.00) slower

[dblock]

Ok, I clearly didn't do my homework, especially on the existing code.