[ruby-core:87244] [Ruby trunk Feature#14784] One-sided Comparable#clamp

[shevegen@gmail.com]

Issue #14784 has been updated by shevegen (Robert A. Heiler).


Considering that Ranges allow a ruby hacker to omit the end value,
for infinity/endless, I think your example makes sense in this
regard, e. g.

    begin .. end

being the same as:

    begin ..

or
    begin..

Perhaps also the converse, but I have to admit that
all these examples look very strange to my eyes. Like:

    clamp(..Date.today)

I always look at it as if something is missing. Personally
I prefer explicit "begin .. end".


The:

    clamp(min: 0, max: 10)

seems to be a nice API, in my opinion. At the least the names "min"
and "max" appear explicit and make sense (to me).

I agree, mostly for consistency, that if endless range has been
accepted, being able to do so via #clamp may seem a logical
continuation (to me). I am mostly neutral to the issue though,
as I do not (yet) use clamp in my own ruby code.

----------------------------------------
Feature #14784: One-sided Comparable#clamp
https://bugs.ruby-lang.org/issues/14784#change-72232

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
**Proposal**

Allow "one-sided" `clamp` to limit only upper bound (and, ideally, only lower too).

Proposed implementation: allow `clamp(begin..end)` call sequence (without deprecating `clamp(begin, end)`), to take advantage from open-ended ranges with `clamp(begin..)`.

**Reasoning about range**

I looked through `#clamp` [discussion](https://bugs.ruby-lang.org/issues/10594), but couldn't find there why syntax `clamp(b, e)` was preferred to `clamp(b..e)`. The only one I could think of is possible confuse of how `clamp(b..e)` and `clamp(b...e)` behaviors should differ.

The problem becomes more important with the introduction of [open-ended ranges](https://bugs.ruby-lang.org/issues/12912). I believe this is pretty natural:

```ruby
some_calculation.clamp(0..)    # now, I use clamp(0, Float::INFINITY)
timestamp.clamp(Date.today..)  # now, I typically use clamp(Date.today..INFINITE_FUTURE_DATE) with custom defined constant
```

Counter-arguments:

1. This is "one-sided", you can't do `clamp(..Date.today)`. To this I can answer than from my experience "clamping only minimum" is more frequent, and if you need to clamp only maximum, most of the time there is some "reasonable minumum". Another idea is that maybe this is a proof why "start-less" ranges are necessary, after all, [doubted here](https://bugs.ruby-lang.org/issues/12912#note-12)
2. Why not just leave current `clamp(b, e)` and allow `clamp(b)`? Answer: because when you see `clamp(10)`, is it `clamp(10, nil)`, or `clamp(nil, 10)` (yes, logically it is the first argument that is left, but from readability point of view it is not that obvious). Possible alternative: `clamp(min: 0, max: 10)`, where you can omit any of two.
3. Why do you need one-sided clamp at all? Because alternatives is much more wordy, making reader think:

```ruby
# with clamp
chain.of.calculations.clamp(0..)

# without clamp
v = chain.of.calculations
v < 0 ? 0 : v

# or, with yield_self (renamed to then)
chain.of.calculations.then { |v| v < 0 ? 0 : v }
```

Both alternatives "without `#clamp`" shows intentions much less clear.



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