From: matz@... Date: 2019-01-10T05:38:00+00:00 Subject: [ruby-core:90968] [Ruby trunk Feature#15483][Rejected] Proc or Method combination with Symbol Issue #15483 has been updated by matz (Yukihiro Matsumoto). Status changed from Open to Rejected I feel the expression `ary.map(&(:to_i << :chr))` is far less readable than `ary.map{|x|x.to_i.chr}`. And the latter is faster and can take arguments NOW e.g. `ary.map{|x|x.to_i(16).chr}`. Given these superiorities, this proposal does not sound attractive. Matz. p.s. And this can lead to the default block parameter like `it`. ---------------------------------------- Feature #15483: Proc or Method combination with Symbol https://bugs.ruby-lang.org/issues/15483#change-76176 * Author: aycabta (aycabta .) * Status: Rejected * Priority: Normal * Assignee: * Target version: ---------------------------------------- In [Feature #6284], Matz said > We need more discussion if we would add combination methods to the Symbol class. Right, let's get started to discuss. For your information, recent a few months I'm discussing this with @osyo . ## This is a discussion of "design" I understand that all features of this issue have both merits and demerits, but I guess that language design is most important. All features of this issue related to each other. ## Abstract At present, you can use `Proc#>>` or `Proc#<<` with `Symbol#to_proc`. ```ruby %w{72 101 108 108 111}.map(&(:to_i.to_proc >> :chr.to_proc)) # => ["H", "e", "l", "l", "o"] ``` This is convenient but methods that take block can take a proc with `&` syntax sugar instead of `#to_proc` by right, like `[1, 2, 3].map(&:to_s)`. So `Symbol#to_proc` looks like too long for `Proc#>>` or `Proc#<<`. Therefore, you need new syntax sugar. ## Receiver ### `Symbol#>>` and `Symbol#<<` `Symbol#>>` and `Symbol#<<` will be considered, but this means that `Symbol` is treated as `Proc` partially. The `[1, 2, 3].map(&:to_s)` treats `Symbol` as `Proc` partially too, but it's with pre-positioned `&`. ```ruby %w{72 101 108 108 111}.map(&(:to_i >> :chr.to_proc)) # => ["H", "e", "l", "l", "o"] ``` I can't come up with other ideas for the `Symbol` receiver. ### New `&:symbol_name` syntax sugar for `:symbol_name.to_proc` ```ruby %w{72 101 108 108 111}.map(&(&:to_i >> :chr.to_proc))) # => ["H", "e", "l", "l", "o"] ``` ## Argument ### Calls `#to_proc` by `Proc#>>` or `Proc#<<` internally as a duck typing ```ruby %w{72 101 108 108 111}.map(&(:to_i.to_proc >> :chr)) # => ["H", "e", "l", "l", "o"] ``` In this case, `Proc#>>`(`:to_i.to_proc >>`) calls `Symbol#to_proc`(for `:chr`) inside. This is useful to use with `Hash#to_proc`: ```ruby h = { Alice: 30, Bob: 60, Cris: 90 } %w{Alice Bob Cris}.map(&(:to_sym.to_proc >> h)) # => [30, 60, 90] ``` ### `Proc#>>` and `Proc#<<` take block as an argument ```ruby %w{72 101 108 108 111}.map(&(:to_i.to_proc >> &:chr)) ``` ## Combination of receiver and argument `Symbol#>>` and calling `#to_proc` internally: ```ruby %w{72 101 108 108 111}.map(&(:to_i >> :chr)) # => ["H", "e", "l", "l", "o"] ``` `&:symbol_name` syntax sugar for `:symbol_name.to_proc` and `Symbol#>>` and taking block: ```ruby %w{72 101 108 108 111}.map(&(&:to_i >> &:chr)) # => ["H", "e", "l", "l", "o"] ``` -- https://bugs.ruby-lang.org/ Unsubscribe: