[swift-evolution] [pitch] Comparison Reform

[Chris Lattner]

> On Apr 17, 2017, at 9:07 AM, Joe Groff via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On Apr 15, 2017, at 9:49 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> For example, I expect `XCTAssertEqual<T : FloatingPoint>(_:_:)` to be vended as part of XCTest, in order to make sure that `XCTAssertEqual(resultOfComputation, Double.nan)` always fails.
> 
> Unit tests strike me as an example of where you really *don't* want level 1 comparison semantics. If I'm testing the output of an FP operation, I want to be able to test that it produces nan when I expect it to, or that it produces the right zero.

I find it very concerning that == will have different results based on concrete vs generic type parameters.  This can only lead to significant confusion down the road.  I’m highly concerned about situations where taking a concrete algorithm and generalizing it (with generics) will change its behavior.

-Chris