Issue #12648 has been updated by Greg L.


In concept, I agree, but, although it's common to return an array from the block, any object can be returned that supports <=>.

Hence, a better solution might be adding a method like `sort_keys` or `sort_key`, where an array is returned by the block, and an array is used as the single parameter for ascending/descending info.  I might suggest, rather than true / false, or :asc / :desc, use 1 for ascending and -1 for descending.

If the parameter array is shorter, remaining keys could default to ascending, if it's longer, it's truncated.

Or (and maybe better), it could just raise an error if the arrays are different length.

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Feature #12648: `Enumerable#sort_by` with descending option
https://bugs.ruby-lang.org/issues/12648#change-59961

* Author: Tsuyoshi Sawada
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
I would like to pass an optional argument to `Enumerable#sort_by` or `Enumerable#sort_by!` to allow descending sort. When the sort key is singular, this could be done by passing a single optinal boolean variable that represents ascending when `false` (default) and descending when `true`:

```ruby
[3, 1, 2].sort_by(&:itself)        # => [1, 2, 3]
[3, 1, 2].sort_by(false, &:itself) # => [1, 2, 3]
[3, 1, 2].sort_by(true, &:itself)  # => [3, 2, 1]
```

When there are multiple sort keys, corresponding numbers of arguments should be passed:

```ruby
[3, 1, 2, 0].sort_by{|e| [e % 2, e]}               # => [0, 2, 1, 3]
[3, 1, 2, 0].sort_by(false, false){|e| [e % 2, e]} # => [0, 2, 1, 3]
[3, 1, 2, 0].sort_by(false, true){|e| [e % 2, e]}  # => [2, 0, 3, 1]
[3, 1, 2, 0].sort_by(true, false){|e| [e % 2, e]}  # => [1, 3, 0, 2]
[3, 1, 2, 0].sort_by(true, true){|e| [e % 2, e]}   # => [3, 1, 2, 0]
```




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