Delphi之前已经重载了好多个ifthen函数
Math单元
function IfThen(AValue: Boolean; const ATrue: Integer; const AFalse: Integer = 0): Integer; overload; inline; function IfThen(AValue: Boolean; const ATrue: Int64; const AFalse: Int64 = 0): Int64; overload; inline; function IfThen(AValue: Boolean; const ATrue: UInt64; const AFalse: UInt64 = 0): UInt64; overload; inline; function IfThen(AValue: Boolean; const ATrue: Single; const AFalse: Single = 0.0): Single; overload; inline; function IfThen(AValue: Boolean; const ATrue: Double; const AFalse: Double = 0.0): Double; overload; inline; function IfThen(AValue: Boolean; const ATrue: Extended; const AFalse: Extended = 0.0): Extended; overload; inline;
StrUtils单元
function IfThen(AValue: Boolean; const ATrue: string; AFalse: string = ”): string; overload; inline;
Delphi从2009之后增加了泛型,那么之前math,strutils单元的ifthen函数有很多种重载形式似乎就可以合并成一个单独的泛型函数了.
type TExtFuns = class class function IfThen<T>(AValue: Boolean; const ATrue, AFalse: T): T; inline; end; class function TExtFuns.IfThen<T>(AValue: Boolean; const ATrue, AFalse: T): T; begin if AValue then Result := ATrue else Result := AFalse; end; //使用示例 var s : string; i : Integer; // s := TExtFuns.IfThen(True, ‘条件成立‘, ‘条件不成立!‘); i := TExtFuns.IfThen(GetTickCount > 1, 1, 2);
从XE3以后扩展了新的Helper语法,可以给任意类型增加扩展函数.就有更方便的技巧了.如下
TBoolHelper = record helper for Boolean function IfThen<T>(const ATrue, AFalse: T): T; inline; end; function TBoolHelper.IfThen<T>(const ATrue, AFalse: T): T; begin if self then Result := ATrue else Result := AFalse; end; //使用 var s : string; i : Integer; // s := True.IfThen(‘a‘,‘b‘); i := (gettickcount >1).IfThen(1, 2); //是不是很爽,方便程度不亚于C语言族系的?:语法吧. end;
XE3之后的SysUtils单元里面内置了TBooleanHelper,TByteBoolHelper,TWordBoolHelper,TLongBoolHelper四个布尔类型的Helper,那么如果易博龙肯把ifthen集成到这四个辅助类上我们用起来就会更方便.只可惜XE5都出了还是没集成在里面。