> On Jul 11, 2015, at 6:29 PM, Roland King <r...@rols.org> wrote:
>
>>
>> However, Roland got it slightly wrong, according to the documentation. This:
>>
>> print (“\(myObj)”)
>>
>> never uses debugDescription, only description. To use debugDescription (if
>> it exists, or description instead):
>>
>> debugPrint (“\(myObj)”)
>
> Dunno about the documentation - I’m remembering a WWDC video which said one
> falls back to the other. So I tested it in a playground. \(variable) appears
> to do as suggested, uses description if that exists, falls back to
> debugDescription if it doesn’t and prints the class name if neither do.
>
> Surprisingly all debugPrint() does is not, as you might expect, use the
> debugDescription in preference, but just puts quotes around the whole thing
> and still uses description if it exists. That feels wrong.
>
> class IHaveNothing{}
>
> class OnlyDebugPrintable : IHaveNothing, CustomDebugStringConvertible
> {
> var debugDescription : String { return "I am
> CustomDebugStringConvertible" }
> }
>
> class HasTheLot : OnlyDebugPrintable, CustomStringConvertible
> {
> var description : String { return "I have the lot" }
> }
>
>
> let a = IHaveNothing()
> let b = OnlyDebugPrintable()
> let c = HasTheLot()
>
> print( "\(a)” ) // IHaveNothing
> print( "\(b)” ) // I am
> CustomDebugStringConvertible
> print( "\(c)” ) // I have the lot
> debugPrint( "\(a)” ) // “IHaveNothing"
> debugPrint( "\(b)” ) // “I am CustomDebugStringConvertible"
> debugPrint( "\(c)” ) // “I have the lot"
Note that there is a distinction between "print an object" and "perform string
interpolation on an object and print that string".
print(c) // I have the lot
print("\(c)") // I have the lot
debugPrint(c) // I am CustomDebugStringConvertible
debugPrint("\(c)") // "I have the lot"
Note that (1) string interpolation prefers the non-debug description when
available, and (2) debugPrint() of a String prints the quotes but print() of a
String does not.
--
Greg Parker gpar...@apple.com Runtime Wrangler
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