变体开发数组参数允许向单个过程或函数传递不同类型表达式的数组。要定义含有变体开放数组参数的例程，需要指定array of const作为参数类型。如，
procedure DoSomething(A: array of const);
这里声明了一个叫做DoSomething的过程，该过程可以操作不同种类的数组。
array of const结构等价于array of TVarRec。TVarRec，在单元System中声明，用于表示一个记录，记录中有一个可以保存多种值（整数、布尔、字符、实数、串、指针、类、类引用、接口、变体等）的变体部分。TVarRec中的VType字段表示数组中每个元素的类型。一些类型作为指针传递而不传递值；特别是长串，作为指针传递并且必需转换为string类型。
下面的例子在函数中使用了变体开放数组参数，该函数对接受的每个元素创建一个串表示法，最后连接成一个串。该函数中调用的串处理例程都定义在SysUtils单元中。
function MakeStr(const Args: array of const): string;
const
BoolChars: array[boolean] of char = ('F', 'T');
var
i: integer;
begin
result := '';
for i := 0 to High(Args) do
with Args[i] do
case VType of
vtInteger: result := result + IntToStr(VInteger);
vtBoolean: result := result + BoolChars[VBoolean];
vtChar: result := result + VChar;
vtExtended: result := result + FloatToStr(VExtended^);
vtString: result := result + VString^;
vtPChar: result := result + VPChar;
vtObject: result := result + VObject.ClassName;
vtClass: result := result + VClass.ClassName;
vtAnsiString: result := result + String(VAnsiString);
vtCurrency: result := result + string(VVariant^);
vtInt64: result := result + IntToStr(VInt64^);
end;
end;
caption := MakeStr(['test', 100, '', true, 3.14159, TForm]);
caption 显示如下：
test100T3.14159TForm
-----------------------------------------------------------------
为说明VInt64之类的，看下面：
特别说明： TVarData和 Variant 具有相同的内存布局!!也就是说，TVarData是对Variant的描述
Delphi syntax:
type
TVarArrayBound = packed record
ElementCount: Integer;
LowBound: Integer;
end;
TVarArrayBoundArray = array [0..0] of TVarArrayBound;
PVarArray = ^TVarArray;
TVarArray = packed record
DimCount: Word;
Flags: Word;
ElementSize: Integer;
LockCount: Integer;
Data: Pointer;
Bounds: TVarArrayBoundArray;
end;
TVarData = packed record
case Integer of
0: (VType: TVarType;
case Integer of
0: (Reserved1: Word;
case Integer of
0: (Reserved2, Reserved3: Word;
case Integer of
varSmallInt: (VSmallInt: SmallInt);
varInteger: (VInteger: Integer);
varSingle: (VSingle: Single);
varDouble: (VDouble: Double);
varCurrency: (VCurrency: Currency);
varDate: (VDate: TDateTime);
varOleStr: (VOleStr: PWideChar);
varDispatch: (VDispatch: Pointer);
varError: (VError: HRESULT);
varBoolean: (VBoolean: WordBool);
varUnknown: (VUnknown: Pointer);
varShortInt: (VShortInt: ShortInt);
varByte: (VByte: Byte);
varWord: (VWord: Word);
varLongWord: (VLongWord: LongWord);
varInt64: (VInt64: Int64);
varString: (VString: Pointer);
varAny: (VAny: Pointer);
varArray: (VArray: PVarArray);
varByRef: (VPointer: Pointer);
);
1: (VLongs: array[0..2] of LongInt);
);
2: (VWords: array [0..6] of Word);
3: (VBytes: array [0..13] of Byte);
);
1: (RawData: array [0..3] of LongInt);
end;
-------------------------------------------------------------------------
觉得复杂，看下面，它说的更清楚直接
----------------------------------------------------------------------
Delphi syntax:
type
PVarRec = ^TVarRec;
TVarRec = record
case Byte of
vtInteger: (VInteger: Integer; VType: Byte);
vtBoolean: (VBoolean: Boolean);
vtChar: (VChar: Char);
vtExtended: (VExtended: PExtended);
vtString: (VString: PShortString);
vtPointer: (VPointer: Pointer);
vtPChar: (VPChar: PChar);
vtObject: (VObject: TObject);
vtClass: (VClass: TClass);
vtWideChar: (VWideChar: WideChar);
vtPWideChar: (VPWideChar: PWideChar);
vtAnsiString: (VAnsiString: Pointer);
vtCurrency: (VCurrency: PCurrency);
vtVariant: (VVariant: PVariant);
vtInterface: (VInterface: Pointer);
vtWideString: (VWideString: Pointer);
vtInt64: (VInt64: PInt64);
end;
C++ syntax:
class TVarRec;
typedef TVarRec* PVarRec;
class TVarRec
{
public:
union
{
Integer VInteger;
Boolean VBoolean;
Char VChar;
PExtended VExtended;
PShortString VString;
Pointer VPointer;
PChar VPChar;
TObject* VObject;
TClass VClass;
WideChar VWideChar;
PWideChar VPWideChar;
Pointer VAnsiString;
PCurrency VCurrency;
PVariant VVariant;
};
union
{
Byte VType;
};
};
//这是在 System 单元定义的一组标识数据类型的常量:
vtInteger = 0;
vtBoolean = 1;
vtChar = 2;
vtExtended = 3;
vtString = 4;
vtPointer = 5;
vtPChar = 6;
vtObject = 7;
vtClass = 8;
vtWideChar = 9;
vtPWideChar = 10;
vtAnsiString = 11;
vtCurrency = 12;
vtVariant = 13;
vtInterface = 14;
vtWideString = 15;
vtInt64 = 16;
//这是定义在 System 单元关于数据类型的一个结构:
TVarRec = record
case Byte of
vtInteger: (VInteger: Integer; VType: Byte);
vtBoolean: (VBoolean: Boolean);
vtChar: (VChar: Char);
vtExtended: (VExtended: PExtended);
vtString: (VString: PShortString);
vtPointer: (VPointer: Pointer);
vtPChar: (VPChar: PChar);
vtObject: (VObject: TObject);
vtClass: (VClass: TClass);
vtWideChar: (VWideChar: WideChar);
vtPWideChar: (VPWideChar: PWideChar);
vtAnsiString: (VAnsiString: Pointer);
vtCurrency: (VCurrency: PCurrency);
vtVariant: (VVariant: PVariant);
vtInterface: (VInterface: Pointer);
vtWideString: (VWideString: Pointer);
vtInt64: (VInt64: PInt64);
end;
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
{把不同数据类型返回字符串的函数}
function Fun1(arr: array of const): string;
var
i: Integer;
begin
Result := '';
for i := Low(arr) to High(arr) do
begin
case arr[i].VType of
vtInteger : Result := Result + IntToStr(arr[i].VInteger) + ' ';
vtBoolean : Result := Result + BoolToStr(arr[i].VBoolean, True) + ' ';
vtChar : Result := Result + arr[i].VChar + ' ';
vtExtended : Result := Result + FloatToStr(arr[i].VExtended^) + ' ';
vtString : Result := Result + PShortString(arr[i].VString)^ + ' ';
vtPointer : Result := Result + IntToStr(Integer(arr[i].VPointer)) + ' ';
vtPChar : Result := Result + arr[i].VPChar + ' ';
vtObject : Result := Result + arr[i].VObject.ClassName + ' ';
vtClass : Result := Result + arr[i].VClass.ClassName + ' ';
vtWideChar : Result := Result + arr[i].VWideChar + ' ';
vtPWideChar : Result := Result + arr[i].VPWideChar + ' ';
vtAnsiString: Result := Result + PAnsiChar(arr[i].VAnsiString)^ + ' ';
vtCurrency : Result := Result + CurrToStr(arr[i].VCurrency^) + ' ';
vtVariant : Result := Result + string(arr[i].VVariant^) + ' ';
vtInterface : Result := Result + IntToStr(Integer(arr[i].VInterface)) + ' ';
vtWideString: Result := Result + PWideChar(arr[i].VWideString) + ' ';
vtInt64 : Result := Result + IntToStr(arr[i].VInt64^) + ' ';
end;
end;
end;
{简化上一个函数}
function Fun2(const arr: array of const): string;
var
i: Integer;
const
n = #32;
begin
Result := '';
for i := Low(arr) to High(arr) do with arr[i] do
begin
case VType of
0 : Result := Result + IntToStr(VInteger) + n;
1 : Result := Result + BoolToStr(VBoolean, True) + n;
2 : Result := Result + VChar + n;
3 : Result := Result + FloatToStr(VExtended^) + n;
4 : Result := Result + PShortString(VString)^ + n;
5 : Result := Result + IntToStr(Integer(VPointer)) + n;
6 : Result := Result + VPChar + n;
7 : Result := Result + VObject.ClassName + n;
8 : Result := Result + VClass.ClassName + n;
9 : Result := Result + VWideChar + n;
10: Result := Result + VPWideChar + n;
11: Result := Result + PAnsiChar(VAnsiString)^ + n;
12: Result := Result + CurrToStr(VCurrency^) + n;
13: Result := Result + string(VVariant^) + n;
14: Result := Result + IntToStr(Integer(VInterface)) + n;
15: Result := Result + PWideChar(VWideString) + n;
16: Result := Result + IntToStr(VInt64^) + n;
end;
end;
end;
{获取类型名的函数}
function Fun3(const arr: array of const): string;
var
i: Integer;
const
n = sLineBreak;
begin
Result := '';
for i := Low(arr) to High(arr) do with arr[i] do
begin
case VType of
0 : Result := Result + 'Integer' + n;
1 : Result := Result + 'Boolean' + n;
2 : Result := Result + 'Char' + n;
3 : Result := Result + 'Extended' + n;
4 : Result := Result + 'String' + n;
5 : Result := Result + 'Pointer' + n;
6 : Result := Result + 'PChar' + n;
7 : Result := Result + 'Object' + n;
8 : Result := Result + 'Class' + n;
9 : Result := Result + 'WideChar' + n;
10: Result := Result + 'PWideChar' + n;
11: Result := Result + 'AnsiString'+ n;
12: Result := Result + 'Currency' + n;
13: Result := Result + 'Variant' + n;
14: Result := Result + 'Interface' + n;
15: Result := Result + 'WideString'+ n;
16: Result := Result + 'Int64' + n;
end;
end;
end;
{测试}
procedure TForm1.Button1Click(Sender: TObject);
var
a: Integer;
b: Boolean;
c: Char;
d: Extended;
e: ShortString;
f: Pointer;
g: PChar;
h: TButton;
i: TClass;
j: WideChar;
k: PWideChar;
l: AnsiString;
m: Currency;
n: Variant;
o: IInterface;
p: WideString;
q: Int64;
begin
a := 1;
b := True;
c := 'a';
d := 2;
e := 'S';
f := Pointer(3);
g := 'P';
h := TButton(Sender);
i := TForm;
j := #19975;
k := '一';
l := 'A';
m := 4;
n := 5;
//o;
p := '我的';
q := 7;
ShowMessage(Fun1([a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q]));
ShowMessage(Fun2([a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q]));
{结果如下:}
{1 True a 2 S 3 P TButton TForm 万 一 A 4 5 0 我的 7 }
ShowMessage(Fun3([a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q]));
{结果如下:
Integer
Boolean
Char
Extended
String
Pointer
PChar
Object
Class
WideChar
PWideChar
AnsiString
Currency
Variant
Interface
WideString
Int64
}
end;
{我试试没有在 TVarRec 中的类型是怎么归类的}
procedure TForm1.Button2Click(Sender: TObject);
var
a: Byte;
b: Word;
c: Cardinal;
d: Double;
e: Real;
f: TStrings;
begin
ShowMessage(Fun3([a,b,c,d,e,f]));
{结果如下:
Integer
Integer
Integer
Extended
Extended
Object
}
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