[ruby-core:99080] [Ruby master Bug#17017] Range#max & Range#minmax incorrectly use Float end as max

[bosticko@gmail.com]

Issue #17017 has been updated by sambostock (Sam Bostock).

Description updated

Add .to_a examples to clarify unexpected behaviour.

----------------------------------------
Bug #17017: Range#max & Range#minmax incorrectly use Float end as max
https://bugs.ruby-lang.org/issues/17017#change-86451

* Author: sambostock (Sam Bostock)
* Status: Open
* Priority: Normal
* ruby -v: 2.7.1
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
While continuing to add edge cases to [`Range#minmax` specs](https://github.com/ruby/spec/pull/777), I discovered the following bug:

```ruby
(1..3.1).to_a.max    == 3      # As expected
(1..3.1).to_a.minmax == [1, 3] # As expected

(1..3.1).max    == 3.1         # Should be 3, as above
(1..3.1).minmax == [1, 3.1]    # Should be [1, 3], as above
```

One way to detect this scenario might be to do (whatever the C equivalent is of)

```ruby
range_end.is_a?(Numeric)                      // Is this a numeric range?
  && (range_end - range_begin).modulo(1) == 0 // Can we reach the range_end using the standard step size (1)
```

As for how to handle it, a couple options come to mind:

- We could error out and do something similar to what we do for exclusive ranges

```ruby
raise TypeError, 'cannot exclude non Integer end value'
```

- We might be able to calculate the range end by doing something like

```ruby
num_steps = (range_end / range_beg).to_i - 1 # one fewer steps than would exceed the range_end
max = range_beg + num_steps                  # take that many steps all at once
```

- We could delegate to `super` and enumerate the range to find the max

```ruby
super
```



-- 
https://bugs.ruby-lang.org/