From: daniel@...42.com
Date: 2019-10-25T14:27:17+00:00
Subject: [ruby-core:95546] [Ruby master Feature#14784] Comparable#clamp with	a range

Issue #14784 has been updated by Dan0042 (Daniel DeLorme).


> 1.clamp(0...3) #=> 1
> 1.clamp(-1...0) # ArgumentError: #clamp with excluding end can't clamp from top -- the only prohibited situation

I don't think it's a good idea for the error to depend on the value being clamped. When Matz said "It should raise an error on end-exclusive ranges" I'm pretty sure it was supposed to mean a simple argument check regardless of the value. Otherwise that code *will* eventually raise an error. Or was that the purpose? In that case the error message should be more like "value out of bounds". But I don't think that's the role/purpose of `clamp`.

----------------------------------------
Feature #14784: Comparable#clamp with a range
https://bugs.ruby-lang.org/issues/14784#change-82322

* Author: zverok (Victor Shepelev)
* Status: Closed
* 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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