An 'in' operator for Ruby?
I have had two fairly small changes I wanted to make in Ruby. The first was realized years ago -- hashes now preserve insertion order and iterate in a predictable way. That's fairly minor, but it did/does have some use cases, and it had no impact on performance.
Here's another one. Personally, this is a bigger thing to me.
I've always believed personally that Ruby should have an
I've mentioned this in speaking (including lightning talks) and in writing. It's not a giant big deal for me, but it is one of my personal favorite ideas. Here are some details.
I propose to let
x in y be syntax sugar for
include? is backwards from common usage -- we don't ask whether a group
includes an item, but whether an item is in a group. The same is true of a
Ruby isn't English; and more generally, programming languages aren't human languages. But programming languages are based on human languages and on everyday experience. We do sometimes ask questions like "Does this container or group include this item?" We are asking a question about the group.
if barrel.include? rotten_apple # Is barrel going bad?
if fruit in [:apple, :pear, :peach] # Is this fruit something I like?
include? is backwards from mathematical usage -- we ask whether a member
is in a set ("epsilon"-like notation), not whether a set contains a memeber.
I ran across someone else a couple of years ago (I wish I could remember who it was!) who bemoaned the absence of this operator. His argument was that he would have a "conversation" with an object, for example, when he tested it repeatedly. Here's a contrived example I just made up.
if foo == var1 || foo =~ var2 || foo < var3 || var4.include?(foo) || foo > var5
To quote him as well as I remember: "I was having this perfectly nice conversation
foo, and then
var4 interrupted it..."
if [GA, VA, MS, TX, MD, NC].include? state # ehhhh if state in [GA, VA, MS, TX, MD, NC] # better
Also a "variable/constant" issue -- I tend to put the
variable data on the left and the constant on right; this is unlike
people who say
if 5 == x. (After all,
5 is only equal to
5 is always equal to 5, even for very large values of 5.)
Also a question of focus: Whatever entity you are really dealing with, name that one first.
Many languages already have an "in" operator -- notably Python, Pascal, even SQL. It is familiar to users of those languages as well as those who use mathematical notation.
in is already a reserved word in Ruby -- used in the
loop (syntax sugar for
each). Let's increase the justification
for its presence.
in operator would sometimes make parentheses unnecessary:
if (10..100).include? x # Need parens if x in 10..100 # Don't need parens (also prettier)
if x.in mylist # ugly if x.== 5 # also ugly if c1.and c2 # ugly (if it worked) if x == 5 # better if c1 and c2 # better if x in mylist # better
?on it. I understand the concept, too, but I find it inappropriate for what is inherently a relational operator.
if x.in? my_set # very ugly if x.==? 5 # very ugly (if it worked)
for x in list? Would this evaluate as
for false? Certainly not. It's a matter of parsing. The
loop itself is just syntax sugar.
I'll bet you like junctions, too. No, in fact, I dislike junctions greatly. I don't even know Perl. Are junctions still a thing?
If you like SQL's
in, you must like
not in also. No, I don't
condone its use of "not in":
if item not in collection # travesty! if ! (item in collection) # ok if x not == y # horrible Ruby travesty (if it worked)
Yes, I say this even though
! (item in collection) requires parentheses.
See the comment about parentheses on ranges.
inat the same level of precedence as the (other) relational operators (
< > <= >=etc.).
People have ignored me on this for at least ten years. They probably still will. That, as they say, is life.