From: eregontp@... Date: 2019-09-22T16:47:24+00:00 Subject: [ruby-core:95035] [Ruby master Feature#16147] List Comprehensions in Ruby Issue #16147 has been updated by Eregon (Benoit Daloze). Just my opinion: I don't think we should have list comprehensions in Ruby. They are just a small subset of the far more powerful Enumerable methods, and IMHO are often less readable (e.g., nested list comprehensions in Python are what I would call unreadable). Also, I think they basically don't scale, they might look nice for small expressions, but as soon as it becomes bigger it's no longer possible to use the list comprehension syntax. So I think it's better to use map/select/filter_map directly. ---------------------------------------- Feature #16147: List Comprehensions in Ruby https://bugs.ruby-lang.org/issues/16147#change-81666 * Author: sammomichael (Samuel Michael) * Status: Open * Priority: Normal * Assignee: * Target version: ---------------------------------------- ## List comprehensions are present in many languages and programmers are quite fond of their simplicity and power. Add to that the fact that Ruby has a for...in loop that is rarely used but could possibly be repurposed. ### Currently we can already do a hack like this to make Ruby support list comprehension syntax: ``` ruby S = [for x in 0...9 do $* << x*2 if x.even? end, $*][1] # [0, 4, 8, 12, 16] ``` Still, it would be far nicer if the for...in loop would return the desired array automatically, this is one way to approach that taking advantage of lambda bracket invocation syntax: ``` ruby c = -> x do $*.clear if x['if'] && x[0] != 'f' . y = x[0...x.index('for')] x = x[x.index('for')..-1] (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << #{y}") x.insert(x.length, "end; $*") eval(x) $*) elsif x['if'] && x[0] == 'f' (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << x") x.insert(x.length, "end; $*") eval(x) $*) elsif !x['if'] && x[0] != 'f' y = x[0...x.index('for')] x = x[x.index('for')..-1] (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << #{y}") x.insert(x.length, "end; $*") eval(x) $*) else eval(x.split[3]).to_a end end ``` so basically we are converting a string to proper ruby syntax for loop then we can use python syntax in a string to do: ``` ruby c['for x in 1..10'] c['for x in 1..10 if x.even?'] c['x**2 for x in 1..10 if x.even?'] c['x**2 for x in 1..10'] # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] # [2, 4, 6, 8, 10] # [4, 16, 36, 64, 100] # [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] ``` -- https://bugs.ruby-lang.org/ Unsubscribe: