Feature #16781: alias :fold :reduce

• Status: Open
• Assignee: -
• Target version: -

1. Method "collect" has short synonym "map", short synonym of "inject" and "reduce" doesn't exist.
2. Name "fold" is more common/popular than "reduce" or "inject".

In my own code I use:

module Enumerable
    alias :fold :reduce
end

I have no idea how to properly add "fold" in Ruby's stdlib/corelib.

• Description updated (diff)

[shan (Shannon Skipper)]

0x81000000 (/ /) wrote:

2. Name "fold" is more common/popular than "reduce" or "inject".

I was surprised to hear this, since I think of "reduce" as most popular. A quick survey of popular languages seems to confirm that "reduce" is most popular, followed by "accumulate."

Reduce:

JavaScript
Python
Java
PHP
Ruby
TypeScript
Swift

Accumulate:

C#
C++

Fold:

Not found

You do also see "fold" in functional languages like Clojure, Scala, Elixir, et cetera, where it has a different meaning than "reduce," which is also present. In any case, "inject" has fallen out of favor.

I have no idea how to properly add "fold" in Ruby's stdlib/corelib.

You could an rb_define_method(rb_mEnumerable, "fold", enum_inject, -1); here: https://github.com/ruby/ruby/blob/v2_7_1/enum.c#L4172-L4173

shan (Shannon Skipper) wrote in #note-2:

I was surprised to hear this, since I think of "reduce" as most popular.

https://en.wikipedia.org/wiki/Fold_(higher-order_function)
Article 'Reduce_(higher-order_function)' - just redirect to link above.

https://www.quora.com/Is-there-a-difference-between-fold-and-reduce-in-functional-languages

C++ STL - bad reference (an example to follow), std::accumulate 4 times slower than for-loop:
https://habr.com/ru/company/dbtc/blog/498374/#comment_21542236