[ruby-core:93205] [Ruby trunk Bug#15929] Array#minmax is much slower than calling both #min and #max

Issue #15929 has been updated by jeremyevans0 (Jeremy Evans).

File array-minmax.patch added

janosch-x (Janosch Mler) wrote:
> possible solutions:
> - a) change `Enumerable#minmax` and let it `rb_funcall` `min` and `max` as suggested [here](https://bugs.ruby-lang.org/issues/15807#note-7) (will also fix 15807)

We cannot use this approach.  `Enumerable#each` can have side effects, and you cannot iterate twice for `minmax` in the general case.  Consider:

```ruby
File.open('...', &:minmax)
```

> - b) implement minmax in array.c to call `rb_ary_min` and `rb_ary_max`

I think this is the correct approach in Array and any other class that overrides `min`/`max`.  Attached is a patch that implements it.

----------------------------------------
Bug #15929: Array#minmax is much slower than calling both #min and #max
https://bugs.ruby-lang.org/issues/15929#change-78653

* Author: janosch-x (Janosch Mler)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.7.0dev
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
this is similar to [issue 15807 about Ranges](https://bugs.ruby-lang.org/issues/15807) and maybe also to [13917](https://bugs.ruby-lang.org/issues/13917)

current situation:

- calling `Array#minmax` incurs a performance penalty of almost 50% compared to calling both `#min` and `#max`

```ruby
require 'benchmark/ips'
arr = (1..1000).map { rand }
Benchmark.ips do |x|
  x.report('min, max') { [arr.min, arr.max] }
  x.report('minmax')   { arr.minmax }
end
```

```
min, max  53.832k (ア 1.8%) i/s -  270.861k in 5.033263s
  minmax  30.093k (ア 1.2%) i/s -  151.980k in 5.051078s
```

background:
- `#minmax` is included via `Enumerable`
- `Enumerable#minmax` does not call array's optimized `#min` and `#max` implementations

possible solutions:
- a) change `Enumerable#minmax` and let it `rb_funcall` `min` and `max` as suggested [here](https://bugs.ruby-lang.org/issues/15807#note-7) (will also fix 15807)
- b) implement minmax in array.c to call `rb_ary_min` and `rb_ary_max`

---Files--------------------------------
array-minmax.patch (2.65 KB)


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