Menu
I'm trying to understand the difference between *(1..9) and [*1..9]
If I assign them to variables they work the same way
splat1 = *(1..9) # splat1 = [1, 2, 3, 4, 5, 6, 7, 8, 9]
splat2 = [*1..9] # splat2 = [1, 2, 3, 4, 5, 6, 7, 8, 9]
But things get weird when I try to use *(1..9) and [*1..9] directly.
*(1..9).map{|a| a.to_s} # syntax error, unexpected '\n', expecting tCOLON2 or '[' or '.'
[*1..9].map{|a| a.to_s} # ["1", "2", "3"...]
I'm guessing part of the problem is with operator precidence? But I'm not exactly sure what's going on. Why am I unable to use *(1..9) the same I can use [*1..9]?
293
As stated by the other answers, the * operator is used to turn an array into an argument list. But what if the object is not an array, as in your case? Then Ruby will call #to_a on the object, if defined, and use the returned array instead. Otherwise, the object itself is used.
A parameter with the splat operator converts the arguments to an array within a method. The arguments are passed in the same order in which they are specified when a method is called. A method can't have two parameters with splat operator.
It is also possible to pass an array as an argument to a method. For example, you might want a method that calculates the average of all the numbers in an array. Your main program might look like this: data = [3.5, 4.7, 8.6, 2.9] average = get_average(data) puts "The average is #{average}."
This can be done in a few ways in Ruby. The first is the plus operator. This will append one array to the end of another, creating a third array with the elements of both. Alternatively, use the concat method (the + operator and concat method are functionally equivalent).
I believe the problem is that splat can only be used as an lvalue, that is it has to be received by something.
So your example of *(1..9).map fails because there is no recipient to the splat, but the [*1..9].map works because the array that you are creating is the recipient of the splat.
UPDATE: Some more information on this thread (especially the last comment): Where is it legal to use ruby splat operator?
62
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
