[swift-evolution] floating point numbers implicit conversion

[Ted F.A. van Gaalen]

> On 19. Jun 2017, at 19:58, Stephen Canon <scanon at apple.com> wrote:
> 
>> On Jun 19, 2017, at 11:46 AM, Ted F.A. van Gaalen via swift-evolution <swift-evolution at swift.org <mailto: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
“temp”  is now a Float
> 	result = temp + double
“temp" being implicitly converted to a Double before expression evaluation 
> 
(assuming the var “result” is still the Float declared in my example)
after conversion, the expression would be implicitly, type wise  
float = Float( double + double)

Apart perhaps from small floating point inherent imprecision, I don’t see much difference...
am I missing something? 

> 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). But there’s a lot more subtlety around them than it seems (for example the C and C++ implicit promotion rules can easily be described on a half-sheet of paper, but are the source of *innumerable* bugs). I would rather have no implicit promotions than half-baked implicit promotions.
> 
I C what you mean. yes, implicit conversion can produce unexpected results, yes.
Have to be used either with common sense or a lot of debugging or both :o)
But that’s the case with many programming language features...
(no debuggers in ca 1980, IDEs are pure luxury :o)

TedvG 

> – Steve

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170619/710e3fb7/attachment.html>