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Ruby 2.3.0 introduces the safe navigation syntax that eases the nil handling of chained method calls by introducing a new operator that only calls the method if value of previous statement is not nil. This is a feature that already exists for example in C#, Groovy and Swift. For example in Groovy, the syntax is
foo?.bar
which basically means that the result value is that of foo.bar unless foo is null, in which case the return value is also null and thus no exception is thrown. Also C# (called null-conditional operators) and Swift (called optional-chaining expression) use this notation.
So the syntax seems to be quite standard in other languages. Now, why in Ruby the syntax is
foo&.bar
instead?
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Safe navigation operator¶ ↑ &. , called “safe navigation operator”, allows to skip method call when receiver is nil . It returns nil and doesn't evaluate method's arguments if the call is skipped.
Use the safe navigation operator ( ?. ) to replace explicit, sequential checks for null references. This operator short-circuits expressions that attempt to operate on a null value and returns null instead of throwing a NullPointerException.
||= is called a conditional assignment operator. It basically works as = but with the exception that if a variable has already been assigned it will do nothing. First example: x ||= 10. Second example: x = 20 x ||= 10. In the first example x is now equal to 10.
This answer is based on the discussion of the feature request in Ruby's issue tracking. According to Ruby's author Yukihiro Matsumoto it wouldn't be possible to introduce operator ?. in Ruby because foo? is valid method name and thus it couldn't be parsed. The first candidate for operator was reversed sequence .?. That syntax was already implemented (by Nobuyoshi Nakada) but was later discarded as it was thought to be too close to original syntax introduced by the other languages (that was not feasible as mentioned earlier). The final syntax &. was accepted as suggested by Matsumoto.
Here's the justification for this syntax given by Matsumoto
I think about this for a while, and thinking of introducing
&.instead of.?, because:
.?is similar to?.in Swift and other languages, but is different anyway.- Since
?is a valid suffix of method names in Ruby, we already see a lot of question marks in our programs.u&.profilereminds us as short form ofu && u.profile.But behavior of
&.should be kept, i.e. it should skipnilbut recognizefalse.
This syntax was then released as part of Ruby 2.3.0-preview1.
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