system.Math和system.StrUtils都有IfThen方法， 返回字符串和 返回 数值型
system.Math.IfThen(vehicle.MILE=0,0,StrToFloat(FormatFloat('0.00',RoundTo(vehicle.MILE,-2))));
system.StrUtils.IfThen(t.Mileage=0,'0',FormatFloat('0.00',RoundTo(t.Mileage,-2)));
Indy中的单元IdGlobal 有iif函数
function iif(ATest: Boolean; const ATrue: Integer; const AFalse: Integer): Integer; overload;
function iif(ATest: Boolean; const ATrue: string; const AFalse: string = ''): string; overload; { do not localize }
function iif(ATest: Boolean; const ATrue: Boolean; const AFalse: Boolean): Boolean; overload;
function iif(const AEncoding, ADefEncoding: TIdTextEncoding; ADefEncodingType: IdAnsiEncodingType = encASCII): TIdTextEncoding; overload;