Feature #15092: Provide step count in Range constructor

• Status: Rejected
• Assignee: -
• Target version: -

[v0dro (Sameer Deshmukh)]

I would like to propose making changes to the Range constructor so that a user can specify
a step count along with start and stop. Since Ruby 2.6 will introduce a step property
in Ranges anyway I think this will be a useful addition.

Here's my reasons for the changes:

When creating software libraries for numerical computing, it is common to query the data
container for values in a particular range at some given steps. For example, say I have the
following NArray object:

a = NArray.new([1,2,3,4,5,6,7,8,9,10,11,12])

And I want the values 1, 4, 7, 10 and 12, I can simply specify a Range like this:

r = Range.new 0, Float::INFINITY, 3 # start, stop (upto the end), step
a[r]
# => NArray([1, 4, 7, 10, 12])

This can possibly also be extended to Array#[] so that users can get ranges of values at
steps without much worry.

[marcandre (Marc-Andre Lafortune)]

• Status changed from Open to Feedback

No need to change the constructor. Instead of:

Range.new 0, Float::INFINITY, 3

Use the shorter

(0...) % 3

[v0dro (Sameer Deshmukh)]

Advantages of changing the constructor:

• Makes it easy to read test code for someone new to Ruby.
• Consistency in specifying step count in constructor (simple and straightforward way) and using
  the shorter syntax (idiomatic Ruby way).

Disadvantages:

• Few extra lines of code to change the constructor.

I think the advantages outweigh the disadvantages.

[duerst (Martin Dürst)]

v0dro (Sameer Deshmukh) wrote:

And I want the values 1, 4, 7, 10 and 12, I can simply specify a Range like this:

r = Range.new 0, Float::INFINITY, 3 # start, stop (upto the end), step
a[r]
# => NArray([1, 4, 7, 10, 12])

Wouldn't the result be [1, 4, 7, 10, 13]?

[v0dro (Sameer Deshmukh)]

Wouldn't the result be [1, 4, 7, 10, 13]?

Ah yes. My bad. Editing the description. Thank you.

[v0dro (Sameer Deshmukh)]

v0dro (Sameer Deshmukh) wrote:

I would like to propose making changes to the Range constructor so that a user can specify
a step count along with start and stop. Since Ruby 2.6 will introduce a step property
in Ranges anyway I think this will be a useful addition.

Here's my reasons for the changes:

When creating software libraries for numerical computing, it is common to query the data
container for values in a particular range at some given steps. For example, say I have the
following NArray object:

a = NArray.new([1,2,3,4,5,6,7,8,9,10,11,12])

And I want the values 1, 4, 7, 10 and 12, I can simply specify a Range like this:

r = Range.new 0, Float::INFINITY, 3 # start, stop (upto the end), step
a[r]
# => NArray([1, 4, 7, 10, 12])

This can possibly also be extended to Array#[] so that users can get ranges of values at
steps without much worry.

The array will return [1,4,7,10]. Sorry for previous mistake.

[shevegen (Robert A. Heiler)]

Wouldn't the result be [1, 4, 7, 10, 13]?

Off-by-one is ... common. :)

A bit more on topic, Float::INFINITY is quite long. Could
we not use :infinity to refer to it in some methods or
something shorter? I think ruby users should not need to
have to know the leading "namespace" (Float) in order to
refer to a concept of infinity in ruby.

[marcandre (Marc-Andre Lafortune)]

v0dro (Sameer Deshmukh) wrote:

Advantages of changing the constructor:

• Makes it easy to read test code for someone new to Ruby.

Very debatable.

• Consistency in specifying step count in constructor (simple and straightforward way) and using
  the shorter syntax (idiomatic Ruby way).

It's actually not consistent, since the result is a Enumerator::ArithmeticSequence, not a Range.

Disadvantages:

• Few extra lines of code to change the constructor.

I realize you wrote "introduces a step property in Ranges anyway I think this will be a useful addition", but this is not true. Range will not have a step property. It's simply that the step method will now return a different class of object that is more useful.

[mrkn (Kenta Murata)]

• Is duplicate of Feature #13904: getter for original information of Enumerator added

[mrkn (Kenta Murata)]

We've already have Emuerator::ArithmeticSequence in trunk.
Please use it.

[v0dro (Sameer Deshmukh)]

OK I'm convinced this is probably a bad idea since step returns an ArithmeticSequence
and is not a property of Range.

Closing the issue.

[mrkn (Kenta Murata)]

• Status changed from Feedback to Rejected