[swift-evolution] String(validatingUTF8:) doesn't

Vladimir.S svabox at gmail.com
Thu Apr 21 05:23:57 CDT 2016

How at all Swift allows such an implicit conversion from one type to 
another, at the same time when we must explicitly convert let say Int8 to 
Int16 ???

I.e. this is not allowed

var i8 : Int8 = 10
var i16 : Int16 = i8

But [Int8] to UnsafePointer<CChar> - no problems.

It is very weird behavior in this case.

Anyone can explain why String(validatingUTF8:) should silently convert 
[Int8] to UnsafePointer<CChar> ??

On 21.04.2016 12:01, Drew Crawford via swift-evolution wrote:
> I have just now for the second time root-caused yet another "nasty nasty UB
> bug" from yet another developer who got cut on the very sharp edge of this API:
>     var result = [40,50,60] as [Int8]
>     return String(validatingUTF8: result)
> This poorly-named String constructor does not take a Swift array of UTF8
> bytes, it takes an UnsafePointer to a C string.  When that C string is not
> null-terminated (as shown here), UB ensues.
> I believe **at least** we need a sane name for this constructor like
> String(validatingUTF8CString:) that vaguely suggests what the programmer
> can do to avoid UB.
> I further believe that this API is just plain bad, but swift-dev disagrees
> and so in the interests of doing /something/ to stop the bleeding I propose
> we rename.
> Drew
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