Stackoverflow-example

ruby_sort_exceptions.rb

require 'ostruct'

# ad 1)
def sort_descending1 _objects, field
  _objects.sort { |b,a| a.send(field) <=> b.send(field) }
end

# ad 2)
def safe_compare2 a,b,field
  a.send(field) <=> b.send(field)
rescue => e
  puts "swallow #{e}"
end

def sort_descending2 _objects, field
  _objects.sort { |b,a| safe_compare2(a,b,field) }
end

# ad 3)
def safe_compare3 a,field,b
  _a,_b = a.send(field), b.send(field)
  _a.class == _b.class ? _a : _a.to_s
end

def sort_descending3 _objects, field
  _objects.sort do |b,a|
    safe_compare3(a,field,b) <=> safe_compare3(b,field,a)
  end
end


# MAIN

objects =  [
  OpenStruct.new( foo: 0 ),
  OpenStruct.new( foo: 1 ),
  OpenStruct.new( foo: 'bar' ),
]

puts "1.) The first attempt"
begin
  puts sort_descending1(objects, :foo).inspect
rescue => e
  puts e.inspect
end

puts "\n2.) Try to catch the error"
begin
  puts sort_descending2(objects, :foo).inspect
rescue => e
  puts e.inspect
end


puts "\n3.) Workaround"
begin
  puts sort_descending3(objects, :foo).inspect
rescue => e
  puts "NEVER REACHED " + e.inspect
end

# OUTPUT
#
#    1.) The first attempt
#    #<ArgumentError: comparison of OpenStruct with OpenStruct failed>
#
#    2.) Try to catch the error
#    #<ArgumentError: comparison of OpenStruct with OpenStruct failed>
#
#    3.) Workaround
#    [#<OpenStruct foo="bar">, #<OpenStruct foo=1>, #<OpenStruct foo=0>]
#



#
# Best solution posted by [@7stud](http://stackoverflow.com/users/926143/7stud) at stackoverflow
#

puts "\n4.) A clean solution"

def safe_compare a, b, field
  result = a.send(field) <=> b.send(field)
  result ||= a.send(field).to_s <=> b.send(field).to_s
end

puts objects.sort { |a,b| safe_compare a,b,:foo }

Note: Line 12, this rescue is not reached.