Delphi: Is it possible to enumerate all instances of a record (~typed constants) in the global namespace?

Question

From the research I've done so far, I'm already guessing the answer is no but just to make sure... (also, this entry can be updated once support for this is available).

The question title should already be self-sufficient I think, but FWIW what I'm trying to do is this: I have a configuration framework built around record constants: Every configuration option available in my app is defined in a central place in the form of a typed constant, which contains the name of the registry (or INI) key, its data type and its default value. These constants are what I pass to the accessor methods in my framework which then implements the necessary logic for retrieving and storing the option values.

I'd now like to extend the information in those records to also include meta data that I can use to auto-generate ADM/ADMX files (ifdef'ed out in the release builds) describing those options.

But for that I'd need to be able to enumerate those constants, unless I add some sort of explicit registration mechanism which seems like unnecessary duplication.

Ideally, instead of adding additional fields to the record type I would have preferred to declare the meta info in the form of attributes but those cannot (yet?) be applied to constants. Also, this wouldn't change anything about the necessity of enumerating the constants in the first place.

Assuming that this currently isn't possible via RTTI, I will probably consider putting the meta data into comments and somehow parsing that out. That'll likely be another question here.

[platform info: currently using Delphi 2010, but I already have an XE license - just didn't have time to install it, yet]

Answer 1

_{Long answer coming up .... :-)}

Instead of trying to enumerate global constants, you might want to try a different approach to what you're doing.

Some time ago, Robert Love had a very interesting idea. He uses custom attributes and RTTI to specify how to store and retrieve values from a .ini file.

In his blog he's got a great explanation on how it works:

http://robstechcorner.blogspot.com/2009/10/ini-persistence-rtti-way.html

---

I've expanded on that a bit in the code below:

• You can now have other types than strings only (string, integer, double, boolean).
• You can specify a default value in your attributes.
• There's a base settings class to inherit from. You can set a filename for the inifile here, and it does loading and saving for you.
• Base AppSettings class.. TAppSettings automatically stores settings in a file in this format: <yourappname>.config.ini

Example... When I want to have database settings stored in an ini file, all I need to do is instantiate a TDbSettings. You don't need to know how or where the values are actually stored, and access is really fast.

var 
  DbSettings : TDbSettings
begin
  DbSettings := TDbSettings.Create;
  try
    // show some settings
    WriteLn(DbSettings.Host);
    WriteLn(DbSettings.Port);
    // write setting
    DbSettings.UserName := 'Me';
    // store it in the ini file
    DbSettings.Save;
  finally
    DbSettings.Free;
  end;
end;

---

If you want to specify a new set of settings, it's really easy.

  TServiceSettings=class(TAppSettings)
  public
    [IniValue('Service','Description','MyServiceDesc')]
    ServiceDescription: String;

    [IniValue('Service','DisplayName','MyServiceName')]
    ServiceDisplayName: String;
  end;

This is so much cleaner than directly reading and writing an inifile. Robert, if you read this: thanks for making my life much easier!

Here's the updated code:

unit WvN.Configuration.Persist.Ini;
// MIT License
//
// Copyright (c) 2009 - Robert Love
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE
//
// Wouter van Nifterick: 2010-11: added TSettings abstract class and some derivatives to load database and cs settings
interface
uses SysUtils,Classes, Rtti,TypInfo;

type
  IniValueAttribute = class(TCustomAttribute)
  private
    FName: string;
    FDefaultValue: string;
    FSection: string;
  public
     constructor Create(const aSection : String;const aName : string;const aDefaultValue : Integer = 0);overload;
     constructor Create(const aSection : String;const aName : string;const aDefaultValue : Double = 0.0);overload;
     constructor Create(const aSection : String;const aName : string;const aDefaultValue : Boolean = false);overload;
     constructor Create(const aSection : String;const aName : string;const aDefaultValue : String = '');overload;
     property Section : string read FSection write FSection;
     property Name : string read FName write FName;
     property DefaultValue : string read FDefaultValue write FDefaultValue;
  end;

  EIniPersist = class(Exception);

  TIniPersist = class (TObject)
  private
    class procedure SetValue(aData : String;var aValue : TValue);
    class function GetValue(var aValue : TValue) : String;
    class function GetIniAttribute(Obj : TRttiObject) : IniValueAttribute;
  public
    class procedure Load(FileName : String;obj : TObject);
    class procedure Save(FileName : String;obj : TObject);
  end;

  TSettings=class abstract(TComponent)
  private
    FOnChange: TNotifyEvent;
    FFileName:String;
    procedure SetOnChange(const Value: TNotifyEvent);
    function GetFileName: String;virtual;
    procedure SetFileName(const Value: String);virtual;
  public
    property FileName:String read GetFileName write SetFileName;
    procedure CreateDefaults;
    procedure Load;virtual;
    procedure Save;virtual;
    constructor Create(AOwner: TComponent); override;
    procedure DoOnChange;
    property OnChange:TNotifyEvent read FOnChange write SetOnChange;
  end;

  TAppSettings=class abstract(TSettings)
    function GetFileName: String;override;
  end;



  TServiceSettings=class(TAppSettings)
  public
    [IniValue('Service','Description','')]
    ServiceDescription: String;

    [IniValue('Service','DisplayName','')]
    ServiceDisplayName: String;
  end;


  TCsSettings=class(TAppSettings)
  public
    [IniValue('CS','SourceAppId',9999)]
    SourceAppId: LongWord;

    [IniValue('CS','SourceCSId',9999)]
    SourceCSId: LongWord;

    [IniValue('CS','Host','Localhost')]
    Host: String;

    [IniValue('CS','Port',42000)]
    Port: LongWord;

    [IniValue('CS','ReconnectInvervalMs',30000)]
    ReconnectInvervalMs: Integer;
  end;

  TFTPSettings=class(TAppSettings)
  public
    [IniValue('FTP','Host','Localhost')]
    Host: String;

    [IniValue('FTP','Port',21)]
    Port: LongWord;

    [IniValue('FTP','RemotePath','/')]
    RemotePath: String;

    [IniValue('FTP','LocalPath','.')]
    LocalPath: String;

    [IniValue('FTP','Username','')]
    Username: String;

    [IniValue('FTP','Password','')]
    Password: String;

    [IniValue('FTP','BlockSize',4096)]
    BlockSize: Cardinal;
  end;


  TDbSettings=class(TAppSettings)
  private
    function GetURL: String;
  public
    [IniValue('DB','Host','Localhost')]
    Host: String;

    [IniValue('DB','Port',3306)]
    Port: LongWord;

    [IniValue('DB','Database','')]
    Database: String;

    [IniValue('DB','Username','root')]
    Username: String;

    [IniValue('DB','Password','')]
    Password: String;

    [IniValue('DB','Protocol','mysql-5')]
    Protocol: String;

    [IniValue('DB','UseSSL',True)]
    UseSSL: Boolean;

    [IniValue('DB','Compress',True)]
    Compress: Boolean;

    [IniValue('DB','TimeOutSec',0)]
    TimeOutSec: Integer;

    [IniValue('DB','SSL_CA','U:\Efkon2\AMM_mysql_cas.crt')]
    SSL_CA: String;

    [IniValue('DB','SSL_CERT','U:\Efkon2\AMM_ARS_mysql_user.pem')]
    SSL_CERT: String;

    [IniValue('DB','SSL_KEY','U:\Efkon2\AMM_ARS_mysql_user_key.pem')]
    SSL_KEY: String;

    property URL:String read GetURL;
  end;

  TPathSettings=class(TAppSettings)
  public

    [IniValue('Paths','StartPath','.')]
    StartPath: String;

    [IniValue('Paths','InPath','In')]
    InPath: String;

    [IniValue('Paths','OutPath','Out')]
    OutPath: String;

    [IniValue('Paths','ErrorPath','Error')]
    ErrorPath: String;
  end;


implementation

uses IniFiles;

{ TIniValue }

constructor IniValueAttribute.Create(const aSection, aName, aDefaultValue: String);
begin
  FSection := aSection;
  FName := aName;
  FDefaultValue := aDefaultValue;
end;

{ TIniPersist }

class function TIniPersist.GetIniAttribute(Obj: TRttiObject): IniValueAttribute;
var
  Attr: TCustomAttribute;
begin
  for Attr in Obj.GetAttributes do
  begin
    if Attr is IniValueAttribute then
    begin
      exit(IniValueAttribute(Attr));
    end;
  end;
  result := nil;
end;

class procedure TIniPersist.Load(FileName: String; obj: TObject);
var
  ctx     : TRttiContext;
  objType : TRttiType;
  Field   : TRttiField;
  Prop    : TRttiProperty;
  Value   : TValue;
  IniValue: IniValueAttribute;
  Ini     : TIniFile;
  Data    : string;
begin
  ctx := TRttiContext.Create;
  try
    Ini := TIniFile.Create(FileName);
    try
      objType := ctx.GetType(Obj.ClassInfo);
      for Prop in objType.GetProperties do
      begin
        IniValue := GetIniAttribute(Prop);
        if Assigned(IniValue) then
        begin
          Data  := Ini.ReadString(IniValue.Section, IniValue.Name, IniValue.DefaultValue);
          Value := Prop.GetValue(Obj);
          SetValue(Data, Value);
          Prop.SetValue(Obj, Value);
        end;
      end;
      for Field in objType.GetFields do
      begin
        IniValue := GetIniAttribute(Field);
        if Assigned(IniValue) then
        begin
          Data  := Ini.ReadString(IniValue.Section, IniValue.Name, IniValue.DefaultValue);
          Value := Field.GetValue(Obj);
          SetValue(Data, Value);
          Field.SetValue(Obj, Value);
        end;
      end;
    finally
      Ini.Free;
    end;
  finally
    ctx.Free;
  end;
end;

class procedure TIniPersist.SetValue(aData: String;var aValue: TValue);
var
  I : Integer;
begin
 case aValue.Kind of
   tkWChar,
   tkLString,
   tkWString,
   tkString,
   tkChar,
   tkUString : aValue := aData;
   tkInteger,
   tkInt64  : aValue := StrToInt(aData);
   tkFloat  : aValue := StrToFloat(aData);
   tkEnumeration:  aValue := TValue.FromOrdinal(aValue.TypeInfo,GetEnumValue(aValue.TypeInfo,aData));
   tkSet: begin
             i :=  StringToSet(aValue.TypeInfo,aData);
             TValue.Make(@i, aValue.TypeInfo, aValue);
          end;
   else raise EIniPersist.Create('Type not Supported');
 end;
end;

class procedure TIniPersist.Save(FileName: String; obj: TObject);
var
  ctx     : TRttiContext;
  objType : TRttiType;
  Field   : TRttiField;
  Prop    : TRttiProperty;
  Value   : TValue;
  IniValue: IniValueAttribute;
  Ini     : TIniFile;
  Data    : string;
begin
  ctx := TRttiContext.Create;
  try
    Ini := TIniFile.Create(FileName);
    try
      objType := ctx.GetType(Obj.ClassInfo);
      for Prop in objType.GetProperties do
      begin
        IniValue := GetIniAttribute(Prop);
        if Assigned(IniValue) then
        begin
          Value := Prop.GetValue(Obj);
          Data  := GetValue(Value);
          Ini.WriteString(IniValue.Section, IniValue.Name, Data);
        end;
      end;
      for Field in objType.GetFields do
      begin
        IniValue := GetIniAttribute(Field);
        if Assigned(IniValue) then
        begin
          Value := Field.GetValue(Obj);
          Data  := GetValue(Value);
          Ini.WriteString(IniValue.Section, IniValue.Name, Data);
        end;
      end;
    finally
      Ini.Free;
    end;
  finally
    ctx.Free;
  end;
end;

class function TIniPersist.GetValue(var aValue: TValue): string;
begin
  if aValue.Kind in [tkWChar, tkLString, tkWString, tkString, tkChar, tkUString,
    tkInteger, tkInt64, tkFloat, tkEnumeration, tkSet] then
    result := aValue.ToString
  else
    raise EIniPersist.Create('Type not Supported');
end;

constructor IniValueAttribute.Create(const aSection, aName: string;
  const aDefaultValue: Integer);
begin
  FSection := aSection;
  FName := aName;
  FDefaultValue := IntToStr(aDefaultValue);
end;

constructor IniValueAttribute.Create(const aSection, aName: string;
  const aDefaultValue: Double);
begin
  FSection := aSection;
  FName := aName;
  FDefaultValue := FloatToStr(aDefaultValue);
end;

constructor IniValueAttribute.Create(const aSection, aName: string;
  const aDefaultValue: Boolean);
begin
  FSection := aSection;
  FName := aName;
  FDefaultValue := BoolToStr(aDefaultValue);
end;

{ TAppSettings }


procedure TSettings.CreateDefaults;
begin
  Load;
  Save;
end;

procedure TSettings.DoOnChange;
begin
  if Assigned(FOnChange) then
    FOnChange(Self)
end;


procedure TSettings.SetOnChange(const Value: TNotifyEvent);
begin
  FOnChange := Value;
end;

{ TAppSettings }

function TAppSettings.GetFileName: String;
begin
  Result := ChangeFileExt(ParamStr(0),'.config.ini')
end;

{ TSettings }

constructor TSettings.Create(AOwner: TComponent);
begin
  inherited;

end;

function TSettings.GetFileName: String;
begin
  Result := FFileName
end;

procedure TSettings.Load;
begin
  TIniPersist.Load(FileName,Self);
  DoOnChange;
end;

procedure TSettings.Save;
begin
  TIniPersist.Save(FileName,Self);
end;

procedure TSettings.SetFileName(const Value: String);
begin
  FFileName := Value
end;


{ TDbSettings }

function TDbSettings.GetURL: String;
begin
  Result := Format('%s://%s:%s@%s:%d/%s?compress=%s&timeout=%d',
  [
    self.Protocol,
    self.Username,
    self.Password,
    self.Host,
    self.Port,
    self.Database,
    booltostr(self.Compress),
    self.TimeOutSec
  ]);
end;

end.