Feature #9076

Updated by nobu (Nobuyoshi Nakada) over 5 years ago


I'd like to introduce a new syntax for blocks that have one argument.

Currently you can do this:

[1, 2, 3].map &:to_s

With the proposed syntax this will be written as:

[1, 2, 3].map &.to_s

Instead of "`:`" ":" we use a "`.`". ".".

The idea is that this new syntax is just syntax sugar that is expanded by the parser to this:

[1, 2, 3].map { |arg| arg.to_s }

This new syntax allows passing arguments:

[1, 2, 3, 4].map &.to_s(2) #=> ["1", "10", "11", "100"]

It also allows chaining calls:

[1, 10, 100].map &.to_s.length #=> [1, 2, 3]

You can also use another block:

[[1, -2], [-3, -4]].map &.map &.abs #=> [[1, 2], [3, 4]]


- Doesn't conflict with any existing syntax, because that now gives a syntax error, so it is available.
- Allows passing arguments and chaining calls
- It's *fast*: it's just syntax sugar. The "`&:to_s`" "&:to_s" is slower because the `to_proc` to_proc method is invoked, you have a cache of procs, etc.
- It looks ok (in my opinion) and allows very nice functional code (like the last example).


- Only supports one (implicit) argument. But this is the same limitation of "`&:to_s`". "&:to_s". If you want more than one argument, use the traditional block syntax.
- It's a new syntax, so users need to learn it. But to defend this point, users right now need to understand the `&:to_s` &:to_s syntax, which is hard to explain (this calls the "`to_proc`" "to_proc" method of Symbol, which creates a block... vs. "it's just syntax sugar for")

What do you think?

We are using this syntax in a new language we are doing, Crystal, which has a syntax very similar to Ruby, and so far we think it's nice, simple and powerful. You can read more about it here: