[swift-evolution] floating point numbers implicit conversion

[David Sweeris]

Sent from my iPhone
> On Jun 19, 2017, at 13:44, John McCall via swift-evolution <swift-evolution at swift.org> wrote:
> 
>>> On Jun 19, 2017, at 1:58 PM, Stephen Canon via swift-evolution <swift-evolution at swift.org> wrote:
>>> On Jun 19, 2017, at 11:46 AM, Ted F.A. van Gaalen via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> var result: Float = 0.0
>>> result = float * integer * uint8 +  double   
>>> // here, all operands should be implicitly promoted to Double before the complete expression evaluation.
>> 
>> You would have this produce different results than:
>> 
>> 	let temp = float * integer * uint8
>> 	result = temp + double
>> 
>> That would be extremely surprising to many unsuspecting users.
>> 
>> Don’t get me wrong; I *really want* implicit promotions (I proposed one scheme for them  way back when Swift was first unveiled publicly).
> 
> I don't!  At least not for floating point.  It is important for both reliable behavior and performance that programmers understand and minimize the conversions they do between different floating-point types.

How expensive is it?

- Dave Sweeris 
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