Is there an "&& Equals" operator in Ruby

Question

I often find myself doing things like this:

do_something if x && x == y

In other works, do something if x is not nil, and it has a value of y.

It would be nice if I could do something like this instead:

do_something if x &&== y

Is there an operator that does this?

Responses to comments:

x == y - The problem with this, is that it only tests existence (not nil) if the value of y is known. If y is itself nil then the check fails. So you could end up doing:

y && x == y

x ||= y - This would assign the value of y to x if x is nil. That's not what I'm looking for. x &&= y doesn't work either for the same reason - it changes the value of x to y if x exists.

An example: in my current scenario I want to check that a user has passed to a controller the token associated with them, but I also want to ensure that the token has been assigned. Something like:

do_something if user.token && user.token == params[:token]

if x has a value, that means it (x) exists, so it is unnecessary, i think. because of unnecessity, there is no such operator. — marmeladze, Sep 01 '16 at 12:35
Assuming `y` has a value, you could just write `... if x == y` — Stefan, Sep 01 '16 at 12:38
@MuntasirAlam that is an _assignment_ operator the OP is looking for a _comparison_ operator, i.e. `==`, not `=`. — Stefan, Sep 01 '16 at 12:43
@Stefan the assumption that `y` has a value is the problem with `if x == y` — ReggieB, Sep 01 '16 at 12:53
That's an odd case, isn't it? It translates to _"do something if `x` is not `nil`, and it has a value of `nil`"_ Are you actually facing this problem? — Stefan, Sep 01 '16 at 12:57
@Stefan in my current scenario I want to check that a user has passed to a controller the token associated with them, but I also want to ensure that the token has been assigned. Something like `if user.token && user.token == params[:token]` — ReggieB, Sep 01 '16 at 13:03
That example helps to understand your problem. You should add it to your question. — Stefan, Sep 01 '16 at 13:05

score 6 · Accepted Answer · edited May 23 '17 at 10:29

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If you are using ruby > 2.3.0 you can use the &. operator: x&.== y. It basically does what .try does in Rails if the value of the operand is different than nil it calls the method and returns its result. If the value is nil it returns nil so you can do things like: do_i_exist&.does_the_result_exist&.nil?

See: What does &. (ampersand dot) mean in Ruby?

edited May 23 '17 at 10:29

Community

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answered Sep 01 '16 at 12:46

hahcho

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Thanks @hakcho. That looks like what I'm looking for. `x &.== y`. Do you know where the `&.` operator is documented. I can't find it in ruby-docs – ReggieB Sep 01 '16 at 12:59
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@ReggieB [Calling Methods](http://ruby-doc.org/core-2.3.1/doc/syntax/calling_methods_rdoc.html#label-Receiver) contains a brief note: _"You may use `&.` to designate a receiver, then `my_method` is not invoked and the result is `nil` when the receiver is `nil`. In that case, the arguments of `my_method` are not evaluated."_ – Stefan Sep 01 '16 at 13:07

Is there an "&& Equals" operator in Ruby

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