On Sun, Jan 31, 2016 at 11:43 AM, Sven Barth <pascaldra...@googlemail.com> wrote:
> Hello together! > > I've finally come around to add a feature that many people have asked > for throughout the years: an inline if that works like the if-statement > in that it only evaluates that expression that is indeed returned. > > After the discussion last year about the inline-if I've decided to add > it as an intrinsic function instead of an extension of the language. > Like all intrinsics it's part of the System unit and "declared" like this: > > === code begin === > > function IfThen(Condition: Boolean; ThenExpr, ElseExpr: type): type; > > === code end === > > Since it's declared in the System unit it won't interfere with the > IfThen()s that are declared in the Math unit or other units, so they'll > continue to work as before to avoid any surprises. > > An important point to note is that in general the result type is > determined by the ThenExpr (there are a few usability exceptions > regarding strings and chars). > > Examples: > > === code begin === > > function A: LongInt; > begin > A := 42; > end; > > function B: LongInt; > B := 21; > end; > > var > i, j: LongInt; > s: String; > begin > i := 42; > j ;= IfThen(i < 32, 48, 21); > > j := IfThen(True, 23, 49); // compiler will warn of unreachable code > j := IfThen(False, 23, 49); // compiler will warn of unreachable code > > j := IfThen(i < 32, A, B); // in this case only B will be executed > > //j := IfThen(i < 32, 32, '123'); // this will fail if there's no > suitable conversion operator available > > //s := IfThen(j < 32, #42, 'Foo'); // this will fail as a char is > expected > s := IfThen(j < 32, #42, #3294); // this will work however and will > result in a WideChar > s := IfThen(j < 32, 'Hello World', 'Hello'#3294'World'); // this will > also work and will result in a WideString (and a warning as s is a > Short-/AnsiString) > end; > > === code end === > > If there are any combinations of types that should work, but do not, > please don't hesistate to report them at http://bugs.freepascal.org/ > Wooow! I did a request about it many years ago, however it was rejected because the limitation in the generic feature at that time. So, I posted a bug related to it yesterday: http://bugs.freepascal.org/view.php?id=29546 Can I use it after this new feature? (I'm upgrading my FPC sources now :-) ) Buddy, thanks a lot for that feature, it is very useful! o/ -- Silvio Clécio
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