[swift-evolution] implementing real (floating point) number comparison tolerance as a compiler directive.

[Joe Groff]

> On Mar 2, 2016, at 1:19 PM, davesweeris at mac.com wrote:
> 
> K… Does replacing my cute == function with one that accounts for everything in that link (or at least a sufficiently large subset of it) solve the problem?

My vague preference is for named methods. In numerics-heavy domains I could see this being valuable enough to burn an operator on.

-Joe

>> On Mar 2, 2016, at 2:56 PM, Joe Groff <jgroff at apple.com <mailto:jgroff at apple.com>> wrote:
>> 
>> 
>>> On Mar 2, 2016, at 12:45 PM, David Sweeris <davesweeris at mac.com <mailto:davesweeris at mac.com>> wrote:
>>> 
>>> func == (lhs: Double, rhs: (value: Double, tolerance: Double)) -> Bool {
>>>     return ((rhs.value - rhs.tolerance)...(rhs.value + rhs.tolerance)) ~= lhs
>>> }
>>> 3.0 == 3.01 ≈ 0.001 // false
>>> 3.0 == 3.01 ≈ 0.01 // true
>>> 
>>> I tried using "ε", which is the standard symbol for "error", but that doesn't seem to be a valid operator character. "≈" (⌥-x, at least on a mac) is the only other one that seemed to make sense, with the possible exception of "∂", but I don't think that's as well-known.
>> 
>> That's cute. In a real implementation of tolerant comparison, you'd want to scale the tolerance to the magnitude of the larger operand, though. (See http://code.jsoftware.com/wiki/Essays/Tolerant_Comparison <http://code.jsoftware.com/wiki/Essays/Tolerant_Comparison> .)
>> 
>> -Joe
> 

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