Array#=== as set equality

Ruby
1

It looks like Array#== and Array#=== are the same. Is that correct?
That being so, would there be any serious consequences if Array#===
were redefined to mean “set equality”, e.g.

[:a,:b] === [:b,:a] #=> true

I can think of a few times that would have been nice to have,
especially when testing and hashes come into play, the results often
do not have a fixed order. e.g.

h = {:a=>1, :b=>2}
r = h.map{ |k,v| [k,v] }

assert r == [[:a,1], [:b,2]]

won’t work b/c it might also return

[[:b,2], [:a,1]]

2

On Wed, Sep 1, 2010 at 11:03 AM, Intransition [email protected]
wrote:

It looks like Array#== and Array#=== are the same. Is that correct?
That being so, would there be any serious consequences if Array#===
were redefined to mean “set equality”, e.g.
I’d prefer
assert r == [[:a,1], [:b,2]]
yup but in your case could you not do something like

assert_equal h, Hash[*r.flatten]

I say that because I’d prefer #=== to have the semantics of include?,
so that I can do

case some_value
when some_array
when other_array
end

Cheers
Robert

3

On Wed, Sep 1, 2010 at 2:03 AM, Intransition [email protected]
wrote:

It looks like Array#== and Array#=== are the same. Is that correct?
That being so, would there be any serious consequences if Array#===
were redefined to mean “set equality”, e.g.

 [:a,:b] === [:b,:a]   #=> true

Well, it breaks existing code that relies on the existing behavior in
case statements (don’t know how common that is), and if it was going
to be redefined, I think it would be more natural to have it reflect
inclusion (like Range#===) so that, e.g.,

[:a,:b] === :a #=> true

OTOH, if you need something that is initialized by a value of a
particular type but provides special match semantics, its pretty
trivial to do; given the number of different things people might want
#=== to do on a particular class, and existing code that depends on
the existing behavior, its usually probably best not to change #===
for existing (especially core) classes, but just to define matcher
classes as needed. E.g.,

class OrderInsensitiveArrayMatcher
def initialize(array)
@array = array.dup
end
def ===(other)
identity = ->(x) {x}
@array.group_by(&identity) == other.group_by(&identity)
rescue
nil
end
end

require ‘set’

class SetMatcher
def initialize(enum)
@set = Set.new(enum)
end
def ===(other)
@set == other.to_set
rescue
nil
end
end

etc.

If there are common use cases, libraries of useful matchers could be
built so that everyone isn’t reinventing the wheel, but without
breaking existing code.

4

On 09/01/2010 06:49 AM, Robert D. wrote:

I say that because I’d prefer #=== to have the semantics of include?,
so that I can do

case some_value
when some_array
when other_array
end

Is an asterisk too much typing?

a = [1,2]
b = [3,4]

case 3
when *a; puts “A”
when *b; puts “B”
end

5

Le 01 septembre à 11:03, Intransition a écrit :

assert r == [[:a,1], [:b,2]]

Well, you’re talking about set semantics. Why not :

r.to_set == [[:b, 2], [:a, 1]].to_set
=> true

?

You could define things like assert_as_set which maps the arguments with
to_set for you, for instance.

(Note that I’m not a regular user of the unit testing frameworks.)

Fred

6

On 09/01/2010 09:01 AM, Benoit D. wrote:

That is rather cool, I did not know splat was working better than
expected here too.

Thanks,
B.D.

Btw, it works in rescue as well.

ALL_NETWORK_ERRORS = [Errno::ECONNRESET, Errno::ECONNABORTED,
Errno::ECONNREFUSED, Errno::EPIPE, IOError, Errno::ETIMEDOUT]

require ‘socket’
begin
TCPSocket.new(“localhost”, 9999)
rescue *ALL_NETWORK_ERRORS => ex
p ex
end

7

On 1 September 2010 17:53, Joel VanderWerf [email protected]
wrote:

Is an asterisk too much typing?

a = [1,2]
b = [3,4]

case 3
when *a; puts “A”
when *b; puts “B”
end

That is rather cool, I did not know splat was working better than
expected here too.

Thanks,
B.D.