Feature #7580: Range translation

• Status: Assigned
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

=begin
I would like to propose the (({#+})) and (({#-})) methods on (({Range})).

These would be useful for translating ranges - for example, given a range where the endpoints are 1-indexed, the range could be translated by 1 in the negative direction to use in (({Array#[]})).

Instead of doing a syntactically-bulky manual translation like so:

ary[(range.begin - 1)..(range.end - 1)]

(({Range#-})) could be used instead:

ary[range - 1]

The translation methods would not handle certain endpoint types specially, they would just pass the call on.

Here's an example implementation in Ruby:

class Range
def +(other)
Range.new(self.begin + other, self.end + other, exclude_end?)
end

def -(other)
  Range.new(self.begin - other, self.end - other, exclude_end?)
end

end

=end

[naruse (Yui NARUSE)]

I think such arithmetic is not addition/subtraction, but shift.

=begin
Do you propose that (({Range#<<})) would use (({#-})) and (({Range#>>})) would use (({#+})), or would it be a different method call internally?

I am happy with both alternatives, I just want nice convenience methods for this operation.
=end

[dummey (Ricky Ng)]

I would normally agree that 'shift' would be the proper term except that it's used in Array already which could cause a bit of confusion.

[naruse (Yui NARUSE)]

• Status changed from Open to Assigned
• Assignee set to matz (Yukihiro Matsumoto)

charliesome (Charlie Somerville) wrote:

Do you propose that (({Range#<<})) would use (({#-})) and (({Range#>>})) would use (({#+})), or would it be a different method call internally?

Don't use +/- and use <</>> or Range#shift().

I am happy with both alternatives, I just want nice convenience methods for this operation.

In my experience, such alternative name considered harmful
because if you want to add another method as Arange#+ in the future, those aliases prevent it.

• Target version set to 2.6

[naruse (Yui NARUSE)]

• Target version deleted (2.6)

[DanielRHeath (Daniel Heath)]

Duplicated at https://bugs.ruby-lang.org/issues/14777

Agree that '+' seems an idiomatic name (I'm using ranges to represent coordinate ranges for bounding boxes).

It's somewhat awkward given that a Range can be eg ('a'..'z') - should ('a'..'z') + 'b' return ('ab'..'zb')?

[DanielRHeath (Daniel Heath)]

On the other hand, + could easily be construed to construct non-contiguous ranges (eg ((1..2) + (4..5)).to_a == [1,2,4,5].