Delphi泛型应用示例之一：接口化指针

来源：互联网发布：wifi定位算法研究编辑：程序博客网时间：2024/05/17 09:24

接口的引用计数特性可以让我们方便地创建一个接口实例，它可以到处使用而无需手动释放内存。但是假如我们这个接口里面有很多数据项那就麻烦多了，得针对每个数据项分别写出其Get和Set方法，接口要写一遍，类还要写一遍。

举个例子，我们想把这个记录类型用接口的方式实现：
TRecord_Test = record
    Data1: string;
    Data2: Integer;
    Data3: Double;
end;

通常的方法是这样的：
type
TInterface_Test = interface
    function GetData1: string;
    function GetData2: Integer;
    function GetData3: Double;
    procedure SetData1(const Value: string);
    procedure SetData2(const Value: Integer);
    procedure SetData3(const Value: Double);
    property Data1: string read GetData1 write SetData1;
    property Data2: Integer read GetData2 write SetData2;
    property Data3: Double read GetData3 write SetData3;
end;

TClass_Test = class(TInterfacedObject, TInterface_Test)
private
    FData2: Integer;
    FData3: Double;
    FData1: string;
    function GetData1: string;
    function GetData2: Integer;
    function GetData3: Double;
    procedure SetData1(const Value: string);
    procedure SetData2(const Value: Integer);
    procedure SetData3(const Value: Double);
public
    property Data1: string read GetData1 write SetData1;
    property Data2: Integer read GetData2 write SetData2;
    property Data3: Double read GetData3 write SetData3;
end;

implementation

{ TClass_Test }
function TClass_Test.GetData1: string;
begin
Result := FData1;
end;

function TClass_Test.GetData2: Integer;
begin
Result := FData2;
end;

function TClass_Test.GetData3: Double;
begin
Result := FData3;
end;

procedure TClass_Test.SetData1(const Value: string);
begin
FData1 := Value;
end;

procedure TClass_Test.SetData2(const Value: Integer);
begin
FData2 := Value;
end;

procedure TClass_Test.SetData3(const Value: Double);
begin
FData3 := Value;
end;

上面的代码是不是看得人吐血？要是有多个类似的记录，恐怕大家宁愿到处维护指针了。
不要紧，我们有万能的泛型。请看下述代码：

unit BambooInterfacedPointer;

interface

type
TValuePointer<T> = packed record
PValue: ^T;
end;

IBambooInterfacedPointer<T> = interface
function Instance: TValuePointer<T>;
end;

TBambooInterfacedPointer<T> = class(TInterfacedObject, IBambooInterfacedPointer<T>)
strict private
    FValuePointer: ^T;
private
    function Instance: TValuePointer<T>; inline;
public
    constructor Create;
    destructor Destroy; override;
end;

implementation

{ TBambooInterfacedPointer<T> }

constructor TBambooInterfacedPointer<T>.Create;
begin
inherited Create;
New(FValuePointer);
System.FillChar(FValuePointer^, SizeOf(T), 0);
end;

destructor TBambooInterfacedPointer<T>.Destroy;
begin
Dispose(FValuePointer);
inherited Destroy;
end;

function TBambooInterfacedPointer<T>.Instance: TValuePointer<T>;
begin
Result.PValue := FValuePointer;
end;

end.

说明一下，之所以要定义
type
TValuePointer<T> = packed record
PValue: ^T;
end;

这么一个东西，是因为在泛型接口里面不允许使用如下写法
IBambooInterfacedPointer<T> = interface
function Instance: ^T;
end;
所以定义了一个记录类型来作为过渡。

最后，则是我写的这个接口化指针的应用实例：

type
TRecord_Test = record
    Data1: string;
    Data2: Integer;
    Data3: Double;
end;

var
aInterfacedPointer: IBambooInterfacedPointer<TRecord_Test>;

begin
aInterfacedPointer := TBambooInterfacedPointer<TRecord_Test>.Create;
with aInterfacedPointer.Instance.PValue^ do
begin
    Data1 := '123';
    Data2 := 456;
    Data3 := 7.89;
end;
end;

是不是很方便啊？重要的是，所有的数据类型都可以这么干！

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