Hello,
I'm not afraid about existing uses of Math.IfThen ou StrUItils.IfThen
because they will hide System.IfThen.
However, existing semantic of IfThen doesn't allow expressions like this
s := IfThen(Obj = nil, 'Unknown', Obj.Value); // raise AV when Obj is nil
As far as I understand, new System.IfThen accepts this kind of code. Good.
But suppose, we add later Math or StrUtils to same unit. This cancel
immediately expected behavior and give AV for IfThen. The only solution
is to specify System.IfThen explicitly (good style of coding but not
used by the most of programmers).
In such case, I would like to propose at least to use other name for
System.IfThen.
IMO, the best solution is don't use a function at all because of
dependency on argument's processing order by compiler. The new operator
will be safe:
s := iif Obj = nil : 'Unknown' : Obj.Value;
Regards,
Serguei
On 31/01/2016 16:20, fpc-pascal-requ...@lists.freepascal.org wrote:
Message: 1
Date: Sun, 31 Jan 2016 15:43:06 +0100
From: Sven Barth<pascaldra...@googlemail.com>
To: FPC-Pascal users discussions<fpc-pascal@lists.freepascal.org>
Subject: [fpc-pascal] New feature: IfThen() intrinsic
Message-ID:<56ae1d7a.5030...@googlemail.com>
Content-Type: text/plain; charset=utf-8
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 athttp://bugs.freepascal.org/
Regards,
Sven
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
