How does the spaceship operator in ruby throws exceptions?

How does the spaceship operator in ruby throws exceptions?

Can anybody explain this strange behavior of exceptions thrown by sort ?
1.) I had the following ruby-code:
def sort_descending _objects, field
_objects.sort { |b,a| a.send(field) <=> b.send(field) }
end
When a.send(field) returns a String and b.send(field) returns an Integer
then an ArgumentError is thrown.
So far, so good.
2.) Next I tried to catch this exception as:
def sort_descending _objects, field
_objects.sort { |b,a| safe_compare(a,b,field) }
end
def safe_compare a, b, field
a.send(field) <=> b.send(field)
rescue
a.send(field).to_s <=> b.send(field).to_s
end
Shouldn't this work?
But this also throws an ArgumentError. I have no idea why?
Can anybody explain this?
Though this workaround works, it looks ugly
def sort_ascending _objects, field
_objects.sort do |a,b|
safe_compare(a,field,b) <=> safe_compare(b,field,a)
end
end
def safe_compare a, field, b
_a,_b = a.send(field), b.send(field)
_a.class == _b.class ? _a : _a.to_s
end
Code to reproduce is at
https://gist.github.com/iboard/6288415#file-ruby_sort_exceptions-rb