if Str = 'Top' then
s := 'Woohoo!'
else
s := 'Climb some more';
While in Delphi we can effectively write this on one line as...
if Str = 'Top' then s := 'Woohoo!' else s := 'Climb some more';
This looks untidy. If we were using another language with immediate if, that would look like this...
s := iif(Str='Top', 'Woohoo!', 'Climb some more');
Now I realise to some Delphi programmers that are not multiple programming language experienced, all that seems a little esoteric but it is standard use in even Excel. Here's how it works...
iif(condition, TrueResult, FalseResult) : String;
The iif() function first looks at the boolean condition. If that condition is true, then it return the TrueResult, and if it is false, then it returns the FalseResult. Here's the declaration
function iif(Test: boolean; TrueR, FalseR: string): string;
The 1st parameter is the Test condition, this can be anything (e.g.: x > y).
The 2nd parameter is the string to return if the test condition is True.
The 3rd parameter is the string to return if the test condition is False.
Here's the full function...
function iif(Test: boolean; TrueR, FalseR: string): string;
begin
if Test then
Result := TrueR
else
Result := FalseR;
end;
but in other languages, the 'type' we return can vary. For example we may want to return 99 if true or 0 of false. How do we do that in Delphi? By using the 'overload' directive.
function iif(Test: boolean; TrueR, FalseR: string): string; overload;
function iif(Test: boolean; TrueR, FalseR: integer): integer; overload;
function iif(Test: boolean; TrueR, FalseR: extended): extended; overload;
Implementation
function iif(Test: boolean; TrueR, FalseR: string): string;
begin
if Test then
Result := TrueR
else
Result := FalseR;
end;
function iif(Test: boolean; TrueR, FalseR: integer): integer;
begin
if Test then
Result := TrueR
else
Result := FalseR;
end;
function iif(Test: boolean; TrueR, FalseR: extended): extended;
begin
if Test then
Result := TrueR
else
Result := FalseR;
end;
We can even extend these to bytes or even TObject if we want to. The only thing we can't do is have the same parameter types and return a different type, e.g...
function iif(Test: boolean; TrueR, FalseR: string): string; overload;
function iif(Test: boolean; TrueR, FalseR: string): integer; overload;
This is a no-no. Why? Delphi will decide which function to run based on the parameter types. If all the parameter types are the same, Delphi will not compile as it will see this as an error.
As already stated, Delphi decides which function it will used based on the types used in the parameters. It will always use the least type for the job. For example, if you have iif()'s set up for both integer and byte, and then use iif(x=y,5,10), then Delphi will use the byte function and return a byte. In most cases this will still work ok even if you are expecting an integer returned.
