Feature #10425: A predicate method to tell if a number is near another

• Status: Open
• Assignee: -
• Target version: -

[sawa (Tsuyoshi Sawada)]

A method near? like the following would be useful.

class Numeric
	def near? other, delta: Float::EPSILON
		(other.to_f - to_f).abs <= delta.to_f
	end
end

class Time
	def near? other, delta: Float::EPSILON
		to_f.near?(other.to_f, delta: delta)
	end
end

It can be used to check errors, or whether something is around something.

23.24324.near?(23.23, delta: 0.5) # => true
t1 = t2 = Time.now
t3 = Time.now
t1.near?(t2) #=> true
t1.near?(t3) #=> false
5.near?(3, delta: 1) #=> true

Some testing frameworks have something similar to this, but I think this is an elementary concept that Ruby should support at it core.

[sawa (Tsuyoshi Sawada)]

The definition above is just to illustrate the functions. There may be a better implementation. Especially, an appropriate error message should be given when an inappropriate argument is given.

error might be a better name to replace the named parameter delta. I am not sure.

[duerst (Martin Dürst)]

Such a predicate would indeed be convenient. But sometimes, one doesn't want to compare with an absolute epsilon, but relatively, e.g. like so:

((other.abs.to_f + abs.to_f) / (other.to_f - to_f).abs) <= ????

[mame (Yusuke Endoh)]

• Related to Feature #15811: Propsing new method for comparing equality of 2 (float) numbers relatively added