A generic cache

Update: Eric Grange suggested a change to TStringList that speeds it up significantly and place it well in front of TCache. I will update the article to reflect this in the end of the week. See the article comments for the details.

In my previous article about a generics based case statement for strings, I commited many sins towards the Church Of Pure Pascal :)

One of them was to not check for prior art. Sergey Antonov aka 0xffff did something similar back in April 2010 (Note: two links!).

So, to make penance for my lack of purity (and have a chance to sin some more), I have tried to take the good parts of the concept and create something less ugly, and more comfortable to use.

I rewrote the generic class and named it TCache. I kept the configurable key type, and I made the lookup value configurable as well. Basically, it all ends up as a thin wrapper around a dictionary, but I quite like the simple declaration you can achieve with this approach.

Example declaration

var
  Cache : TCache<String, Integer>;
  i : Integer;
begin
  if not Assigned(Cache)
  then TCache<String, Integer>
   .Define(Cache, 0)
   ['alpha',   11]
   ['bravo',   22]
   ['charlie', 33]
   ['delta',   44]
   ['echo',    55]
   ['foxtrot', 66];

  i := Cache.Lookup('charlie');

Remember that <String, Integer> can be almost any type you like, including code (for the value part, at least).

Here is the class. Note that I also keep track of the index of the order each key/value was added. This could be removed. Also note that I still do dirty deeds, such as a dangerous cast. I guess I just suck at writing clean code ;).

unit GenericsCache;

/// Written by Lars Fosdal <lars@fosdal.com>, December 5, 2010

interface
uses
  SysUtils, Generics.Collections;

type
  TCacheEntry<T> = record
    Value: T;
    Index: Integer;
  end;

  TCache<KeyT, ValT> = class(TObjectDictionary<KeyT, TCacheEntry<ValT>>)
  private
    FCache: TCache<KeyT, ValT>;
    FDefaultValue: ValT;
    function AddValue(const Id: KeyT; const Value: ValT): TCache<KeyT, ValT>;
  protected
    function ValidateId(Id: KeyT): KeyT; virtual;
  public
    class function Define(var Cache; const aDefaultValue:ValT): TCache<KeyT, ValT>;
    function Lookup(const Id: KeyT):ValT;
    function Index(const Id: KeyT):Integer;
    property DefaultValue: ValT read FDefaultValue write FDefaultValue;
    property Values[const Id: KeyT; const Value: ValT]: TCache<KeyT, ValT> read AddValue; default;
  end;

  TCaseStringCache = class(TCache<String, String>)
    function ValidateId(Id: String): String; override;
  end;

implementation

{ TCache<KeyT, ValT> }

function TCache<KeyT, ValT>.AddValue(const Id: KeyT; const Value: ValT): TCache<KeyT, ValT>;
var
  Rec : TCacheEntry<ValT>;
begin
  Result := Self;
  Rec.Value := Value;
  Rec.Index := Count;
  Add(ValidateId(Id), Rec);
end;

class function TCache<KeyT, ValT>.Define(var Cache; const aDefaultValue: ValT): TCache<KeyT, ValT>;
begin
  Result := Create;
  Result.FCache := Result;
  Result.DefaultValue := aDefaultValue;
  TCache<KeyT, ValT>(Cache) := Result;
end;

function TCache<KeyT, ValT>.Index(const Id: KeyT): Integer;
var
  Rec : TCacheEntry<ValT>;
begin
  if TryGetValue(ValidateId(Id), Rec)
   then Result := Rec.Index
    else Result := -1;
end;

function TCache<KeyT, ValT>.Lookup(const Id: KeyT): ValT;
var
  Rec : TCacheEntry<ValT>;
begin
  if FCache.TryGetValue(ValidateId(Id), Rec)
   then Result := Rec.Value
    else Result := DefaultValue;
end;

function TCache<KeyT, ValT>.ValidateId(Id: KeyT): KeyT;
begin
  Result := Id;
end;

{ TCaseStringCache }

function TCaseStringCache.ValidateId(Id: String): String;
begin
  Result := LowerCase(Id);
end;

end.

I wrote a simple benchmark, testing different ways to use this, and also comparing it to do String2Index / Case -type lookup mechanisms as well as if/then/else, and the ugly method from my previous article. Several people suggested using a string to index / case approach. I have also used that many times. The painful part of strings to index, is that if you change the order of the strings, you also have to change the indices. TCache makes the index entirely optional, since the string is the index - if you see what I mean.

See below for the test code.

The Good, The Bad, and the Ugly.

The test uses GetTickCount and 5.000.000 iterations, for each method, repeated 10 times, with 12 strings (the numbers are consistant at 6 strings as well - except that string to index will be slightly faster) and the process priority was set to High to avoid other parts of the PC affecting the numbers. I weighted the results towards the results for the if/then/else. So Perf tells you how many times slower than if/then/else each test was.

Method	Perf	AvgRun	Comment
TStringSwitch	52.94	35340.7	The ugly was really ugly performance-wise as well.
AnsiIndexTextFunc	12.40	8277.3	String to Index, then case/anon.method is no speed demon either.
StringIndex	12.05	8041.7	Jolyon's variant is around the same speed.
AnsiIndexText	12.03	8032.6	If you remove anon.methods, the impact is not huge.
TStringList	6.94	4631.6	Using a pre-created sorted string list is nearly twice the speed of AnsiIndexText.
TCacheProc	3.70	2471.1	Cool, TCache and anon.methods are nearly twice the speed of a string list.
TCacheFunc	3.71	2475.8	No signficant difference between a procedure and function.
TCacheFuncStack	3.72	2480.5	Passing the anon.method by stack doesn't cost much either.
TCaseStringCache	3.12	2085.6	Case insensitive string to string saves some time over using anon.methods.
TCacheString	2.93	1957.9	So does eliminating the LowerCase function. TCache with string/string is 3 times slower than if/then/else, but it is 4 times faster than AnsiIndexText, and more than twice as fast as a string list.
If/then/else	1	667.6	You can't beat this. You also can't enjoy maintaining it.
LastKey	0.39	260.4	No surprise that indexed array lookups are fast. Yes, I know I am not looking up the same strings, but the cost is the same.

If you need to repeatedly do lookup by strings, you can benefit from using something like TCache. Also - for the AnsiIndexText - it does a sequential search for the match, hence if the list is long, or the later entries are more commonly used - it will degrade performancewise. Without having dissected TDictionary in detail, I would believe that it's hash table will allow TCache to remain relativly constant in performance, even if you add thousands of entries.

You could also shave off some more by eliminating the ValidateId methods.

Here is the test program (which also use the unit from my previous article).

program TestGenericsSwitch;
{$apptype Console}
uses
  ExceptionLog,
  Windows,
  Classes,
  SysUtils,
  StrUtils,
  GenericsCache in 'GenericsCache.pas',
  GenericsSwitch in 'GenericsSwitch.pas';

{$define Twelve}  // remove this to run with 6 strings

const
  {$ifndef Twelve}
  Elements = 6;
  {$else}
  Elements = 12;
  {$endif}
  TestCount = 5000000;
  Keys : Array[0..Elements] of String
   = ('alpha','bravo', 'charlie', 'delta', 'echo', 'foxtrot',
  {$ifdef Twelve}
      'golf', 'hotel', 'india', 'juliet', 'kilo', 'lima',
  {$endif}
      'what');

type
  TFunc = reference to function:String;
  TProc = reference to procedure;

function RandomKey:String;
begin
  Result := Keys[Random(Elements + 1)];
end;

function AssignTest:String;
var
  ix : Integer;
  s: String;
begin
  for ix := 0 to TestCount - 1
  do TStringSwitch.CaseOf(RandomKey)
    ['alpha', procedure begin
            s := 'Definitively any case';
          end]
    ['bravo', procedure begin
            s := 'B all you can B';
          end]
    ['charlie', procedure begin
            s := 'Checkpoint C';
          end]
    ['delta', procedure begin
            s := 'Checkpoint D';
          end]
    ['echo', procedure begin
            s := 'Checkpoint E';
          end]
    ['foxtrot', procedure begin
            s := 'Checkpoint F';
          end]
{$ifdef Twelve}
    ['golf', procedure begin
            s:= 'golf';
          end]
    ['hotel',procedure begin
            s:= 'hotel';
          end]
    ['india',procedure begin
            s:= 'india';
          end]
    ['juliet', procedure begin
            s:= 'juliet';
          end]
    ['kilo', procedure begin
            s:= 'kilo';
          end]
    ['lima', procedure begin
            s:= 'lima';
          end]
{$endif}
    .ElseCase(procedure begin
            s := 'Else what?';
          end)
    .EndCase;
  Result := s;
end;

function AssignTestIf:String;
var
  ix : Integer;
  s, t: String;
begin
  for ix := 0 to TestCount - 1 do
  begin
    t := LowerCase(RandomKey);
    if t = 'alpha' then
      s := 'Definitively any case'
    else if t = 'bravo' then
      s := 'B all you can B'
    else if t = 'charlie' then
      s := 'Checkpoint C'
    else if t = 'delta' then
      s := 'Checkpoint D'
    else if t = 'echo' then
      s := 'Checkpoint E'
    else if t = 'foxtrot' then
      s := 'Checkpoint F'
{$ifdef Twelve}
    else if t = 'golf' then
      s := 'golf'
    else if t = 'hotel' then
      s := 'hotel'
    else if t = 'india' then
      s := 'india'
    else if t = 'juliet' then
      s := 'juliet'
    else if t = 'kilo' then
      s := 'kilo'
    else if t = 'lima' then
      s := 'lima'
{$endif}
    else
      s := 'Else what?';
  end;
  Result := s;
end;

function AssignTestS2I:String;
var
  ix : Integer;
  s: String;
begin
  for ix := 0 to TestCount - 1
  do case AnsiIndexText(RandomKey, ['alpha', 'bravo', 'charlie', 'delta', 'echo', 'foxtrot'
{$ifdef Twelve}
    , 'golf', 'hotel', 'india', 'juliet', 'kilo', 'lima'
{$endif}
  ]) of
    0 : s := 'Definitively any case';
    1 : s := 'B all you can B';
    2 : s := 'Checkpoint C';
    3 : s := 'Checkpoint D';
    4 : s := 'Checkpoint E';
    5 : s := 'Checkpoint F';
{$ifdef Twelve}
    6 : s := 'golf';
    7 : s := 'hotel';
    8 : s := 'india';
    9 : s := 'juliet';
   10 : s := 'kilo';
   11 : s := 'lima';
{$endif}
   else s := 'Else what?';
  end;
  Result := s;
end;

function StringIndex(const aString: string; const aCases: array of string;
  const aCaseSensitive: Boolean): Integer;
begin
  if aCaseSensitive then
  begin
    for Result := 0 to Pred(Length(aCases)) do
      if ANSISameText(aString, aCases[Result]) then
        EXIT;
  end
  else
  begin
    for Result := 0 to Pred(Length(aCases)) do
      if ANSISameStr(aString, aCases[Result]) then
        EXIT;
  end;

  Result := -1;
end;

function AssignStringIndexFunc:String;
var
  ix : Integer;
  func : TFunc;
begin
  for ix := 0 to TestCount - 1
  do case StringIndex(RandomKey, ['alpha', 'bravo', 'charlie', 'delta', 'echo', 'foxtrot'
  {$ifdef Twelve}
    , 'golf', 'hotel', 'india', 'juliet', 'kilo', 'lima'
  {$endif}], false) of
    0 : func := function:String begin
          Result := 'Definitively any case';
        end;
    1 : func := function:String begin
          Result := 'B all you can B';
        end;
    2 : func := function:String begin
          Result := 'Checkpoint C';
        end;
    3 : func := function:String begin
          Result := 'Checkpoint D';
        end;
    4 : func := function:String begin
          Result := 'Checkpoint E';
        end;
    5 : func := function:String begin
          Result := 'Checkpoint F';
        end;
{$ifdef Twelve}
    6 : func := function:String begin
          Result:= 'golf';
        end;
    7 : func := function:String begin
          Result:= 'hotel';
        end;
    8 : func := function:String begin
          Result:= 'india';
        end;
    9 : func := function:String begin
          Result:= 'juliet';
        end;
    10: func := function:String begin
          Result:= 'kilo';
        end;
    11: func := function:String begin
          Result:= 'lima';
        end;
{$endif}
   else func := function:String begin
         Result := 'Else what?';
       end;
  end;
  Result := Func;
end;

function AssignTestS2IFunc:String;
var
  ix : Integer;
  func : TFunc;
begin
  for ix := 0 to TestCount - 1
  do case AnsiIndexText(RandomKey, ['alpha', 'bravo', 'charlie', 'delta', 'echo', 'foxtrot'
  {$ifdef Twelve}
    , 'golf', 'hotel', 'india', 'juliet', 'kilo', 'lima'
  {$endif}]) of
    0 : func := function:String begin
          Result := 'Definitively any case';
        end;
    1 : func := function:String begin
          Result := 'B all you can B';
        end;
    2 : func := function:String begin
          Result := 'Checkpoint C';
        end;
    3 : func := function:String begin
          Result := 'Checkpoint D';
        end;
    4 : func := function:String begin
          Result := 'Checkpoint E';
        end;
    5 : func := function:String begin
          Result := 'Checkpoint F';
        end;
{$ifdef Twelve}
    6 : func := function:String begin
          Result:= 'golf';
        end;
    7 : func := function:String begin
          Result:= 'hotel';
        end;
    8 : func := function:String begin
          Result:= 'india';
        end;
    9 : func := function:String begin
          Result:= 'juliet';
         end;
    10: func := function:String begin
          Result:= 'kilo';
        end;
    11: func := function:String begin
          Result:= 'lima';
        end;
{$endif}
   else func := function:String begin
         Result := 'Else what?';
       end;
  end;
  Result := Func;
end;

function AssignCaseStringCache:String;
var
  ix : Integer;
  s: String;
  Cache : TCaseStringCache;
begin
  TCaseStringCache.Define(Cache,
               'Else what?')
   ['alpha',   'Definitively any case']
   ['bravo',   'B all you can B']
   ['charlie', 'Checkpoint C']
   ['delta',   'Checkpoint D']
   ['echo',    'Checkpoint E']
   ['foxtrot', 'Checkpoint F']
{$ifdef Twelve}
   ['golf', 'golf']
   ['hotel', 'hotel']
   ['india', 'india']
   ['juliet', 'juliet']
   ['kilo', 'kilo']
   ['lima', 'lima']
{$endif};
  for ix := 0 to TestCount - 1
   do s := Cache.Lookup(RandomKey);
  Result := s;
end;

function AssignCacheString:String;
var
  ix : Integer;
  s: String;
  Cache : TCache< String, String>;
begin
  TCache<String, String>
   .Define(Cache, 'Else what?')
   ['alpha',   'Definitively any case']
   ['bravo',   'B all you can B']
   ['charlie', 'Checkpoint C']
   ['delta',   'Checkpoint D']
   ['echo',    'Checkpoint E']
   ['foxtrot', 'Checkpoint F']
{$ifdef Twelve}
   ['golf', 'golf']
   ['hotel', 'hotel']
   ['india', 'india']
   ['juliet', 'juliet']
   ['kilo', 'kilo']
   ['lima', 'lima']
{$endif};
  for ix := 0 to TestCount - 1
   do s := Cache.Lookup(RandomKey);
  Result := s;
end;

function AssignCacheProc:String;
var
  ix : Integer;
  s: String;
  Cache : TCache<String, TProc>;
begin
  TCache<String, TProc>.Define(Cache,
               procedure begin
                 s := 'Else what?';
               end)
   ['alpha',     procedure begin
                 s := 'Definitively any case';
               end]
   ['bravo',   procedure begin
                 s := 'B all you can B';
               end]
   ['charlie', procedure begin
                 s := 'Checkpoint C';
               end]
   ['delta',   procedure begin
                 s := 'Checkpoint D';
               end]
   ['echo',    procedure begin
                 s := 'Checkpoint E';
               end]
   ['foxtrot', procedure begin
                 s := 'Checkpoint F';
               end]
{$ifdef Twelve}
    ['golf',   procedure begin
                 s:= 'golf';
               end]
    ['hotel',  procedure begin
                 s:= 'hotel';
               end]
    ['india',  procedure begin
                 s:= 'india';
               end]
    ['juliet', procedure begin
                 s:= 'juliet';
               end]
    ['kilo',   procedure begin
                 s:= 'kilo';
               end]
    ['lima',   procedure begin
                 s:= 'lima';
               end]
{$endif};

  for ix := 0 to TestCount - 1
   do Cache.Lookup(RandomKey)();
  Result := s;
end;

function AssignCacheFuncStack:String;
var
  ix : Integer;
  s: String;
  Cache : TCache<String, TFunc>;
begin
  TCache<String, TFunc>.Define(Cache,
               function:String begin
                 Result := 'Else what?';
               end)
   ['alpha',     function:String begin
                 Result := 'Definitively any case';
               end]
   ['bravo',   function:String begin
                 Result := 'B all you can B';
               end]
   ['charlie', function:String begin
                 Result := 'Checkpoint C';
               end]
   ['delta',   function:String begin
                 Result := 'Checkpoint D';
               end]
   ['echo',    function:String begin
                 Result := 'Checkpoint E';
               end]
   ['foxtrot', function:String begin
                 Result := 'Checkpoint F';
               end]
{$ifdef Twelve}
    ['golf', function:String begin
            Result := 'golf';
          end]
    ['hotel',function:String begin
            Result := 'hotel';
                 end]
    ['india',function:String begin
            Result := 'india';
                 end]
    ['juliet', function:String begin
            Result := 'juliet';
          end]
    ['kilo', function:String begin
            Result := 'kilo';
          end]
    ['lima', function:String begin
            Result := 'lima';
          end]
{$endif};

  for ix := 0 to TestCount - 1
   do s := Cache.Lookup(RandomKey)();
  Result := s;
end;

function AssignCacheFunc:String;
var
  ix : Integer;
  s: String;
  func: TFunc;
  Cache : TCache<String, TFunc>;
begin
  TCache<String, TFunc>.Define(Cache,
               function:String begin
                 Result := 'Else what?';
               end)
   ['alpha',     function:String begin
                 Result := 'Definitively any case';
               end]
   ['bravo',   function:String begin
                 Result := 'B all you can B';
               end]
   ['charlie', function:String begin
                 Result := 'Checkpoint C';
               end]
   ['delta',   function:String begin
                 Result := 'Checkpoint D';
               end]
   ['echo',    function:String begin
                 Result := 'Checkpoint E';
               end]
   ['foxtrot', function:String begin
                 Result := 'Checkpoint F';
               end]
{$ifdef Twelve}
    ['golf', function:String begin
            Result := 'golf';
          end]
    ['hotel',function:String begin
            Result := 'hotel';
                 end]
    ['india',function:String begin
            Result := 'india';
                 end]
    ['juliet', function:String begin
            Result := 'juliet';
          end]
    ['kilo', function:String begin
            Result := 'kilo';
          end]
    ['lima', function:String begin
            Result := 'lima';
          end]
{$endif};

  for ix := 0 to TestCount - 1
   do begin
     func := Cache.Lookup(RandomKey);
     s := func;
   end;
  Result := s;
end;

function AssignStringList:String;
var
  ix, fx : Integer;
  s: String;
  func : TFunc;
  obj : TObject absolute func;
  StrList : TStringList;
begin
  StrList := TStringList.Create;

  StrList.AddObject('alpha', TObject(function:String begin
                 Result := 'Definitively any case';
               end));
  StrList.AddObject('bravo', TObject(function:String begin
                 Result := 'B all you can B';
               end));
  StrList.AddObject('charlie', TObject(function:String begin
                 Result := 'Checkpoint C';
               end));
  StrList.AddObject('delta', TObject(function:String begin
                 Result := 'Checkpoint D';
               end));
  StrList.AddObject('echo', TObject(function:String begin
                 Result := 'Checkpoint E';
               end));
  StrList.AddObject('foxtrot', TObject(function:String begin
                 Result := 'Checkpoint F';
               end));
//{$ifdef Twelve}
  StrList.AddObject('golf', TObject(function:String begin
            Result := 'golf';
          end));
  StrList.AddObject('hotel',TObject(function:String begin
            Result := 'hotel';
                 end));
  StrList.AddObject('india',TObject(function:String begin
            Result := 'india';
                 end));
  StrList.AddObject('juliet', TObject(function:String begin
            Result := 'juliet';
          end));
  StrList.AddObject('kilo', TObject(function:String begin
            Result := 'kilo';
          end));
  StrList.AddObject('lima', TObject(function:String begin
            Result := 'lima';
          end));
//{$endif}

  StrList.Sorted := True;

  for ix := 0 to TestCount - 1
   do begin
     fx := StrList.IndexOf(RandomKey);
     if fx >= 0
      then begin
        obj := StrList.Objects[fx];
        s := func;
      end
       else s := 'ElseWhat';
   end;
  Result := s;
end;

function TimeIt(proc: TFunc; name:String):Integer;
var
  start : Cardinal;
  LastLookup : String;
  oldSeed : Integer;
begin
  OldSeed := RandSeed;
  start := GetTickCount;
  LastLookup := Proc;
  Result := GetTickCount - start;
  Writeln(Format('%-18s %6d - %s', [name, Result, LastLookup]));
  RandSeed := OldSeed;
end;

function LastKey:String;
var
  ix : Integer;
  s : String;
  OldSeed : Integer;
begin
  OldSeed := RandSeed;
  for ix := 0 to TestCount - 1
   do s := RandomKey;
  RandSeed := OldSeed;
  Result := s;
end;

procedure Test;
const
  Repeats = 10;
var
  ix : Integer;
begin
  for ix := 0 to Repeats - 1
  do begin
    Randomize;
//    RandSeed := 2003112605;
    Writeln;
    Writeln(Format('strings=%d, repeats=%d, seed=%d', [Elements, TestCount, RandSeed]));
    TimeIt(AssignTest,'TStringSwitch');
    TimeIt(AssignTestS2IFunc, 'AnsiIndexText Func');
    TimeIt(AssignStringIndexFunc, 'StringIndex');
    TimeIt(AssignTestS2I, 'AnsiIndexText');
    TimeIt(AssignStringList,'TStringList');
    TimeIt(AssignCacheProc, 'TCache Proc');
    TimeIt(AssignCacheFunc, 'TCache Func');
    TimeIt(AssignCacheFuncStack, 'TCache Func Stack');
    TimeIt(AssignCaseStringCache, 'TCaseStringCache');
    TimeIt(AssignCacheString, 'TCache String');
    TimeIt(AssignTestIf, 'If/then/else');
    TimeIt(LastKey, 'LastKey');
  end;
end;

begin
  try
    Write('Press Enter to start: ');
    Readln;

    Test;

  finally
    Writeln;
    Write('Press Enter: ');
    Readln;
  end;
end.

A generic case for strings

Do you remember the discussion about a case statement for strings?

I got this flash idea after reading Jolyon Smith's "The case for case[]", and remembering a comment from Francisco Ruiz on Nick Hodges' article on THTMLWriter which suggested using a default array property in a creative fashion.

Honestly, it is not really a true case statement, and it might not be as fast as an if then else, but here is how it looks when used. A bit ugly. but good fun :)

program TestGenericsSwitch;
{$apptype Console}
uses
  GenericsSwitch;
begin
  TStringSwitch.CaseOf('chARLie')
    ['Any', procedure begin
            Writeln('Definitively any case');
          end]
    ['B', procedure begin
            Writeln('B all you can B');
          end]
    ['Charlie', procedure begin
            Writeln('Checkpoint C');
          end]
    .ElseCase(procedure begin
            Writeln('Else what?');
          end)
    .EndCase;
end.

And here is how it is implemented.

unit GenericsSwitch;

/// Written by Lars Fosdal <lars@fosdal.com>, December 1, 2010

interface
uses
  SysUtils, Generics.Collections;

type
  TSwitchProc = reference to procedure;
  TGenericSwitch<KeyType> = class(TObjectDictionary<KeyType, TSwitchProc>)
  private
    FTheElseCase: TSwitchProc;
    FTheTargetKey: KeyType;
    function AddSwitchCase(const name: KeyType; 
                           const value: TSwitchProc): TGenericSwitch<KeyType>;
    procedure SetTheElseCase(const Value: TSwitchProc);
    procedure SetTheTargetKey(const Value: KeyType);
  protected
    function ValidateKey(Key:KeyType):KeyType; virtual;
    property TheTargetKey:KeyType read FTheTargetKey write SetTheTargetKey;
    property TheElseCase:TSwitchProc read FTheElseCase write SetTheElseCase;
  public
    class function CaseOf(const Key: KeyType):TGenericSwitch<KeyType>;
    function ElseCase(const Action: TSwitchProc): TGenericSwitch<KeyType>;
    procedure EndCase;
    property Cases[const name:KeyType; const value:TSwitchProc]: TGenericSwitch<KeyType>
                  read AddSwitchCase; default;
  end;

  TStringSwitch = class(TGenericSwitch<String>)
    function ValidateKey(key:String):String; override;
  end;

implementation

{ TGenericSwitch<KeyType, TSwitchProc> }

function TGenericSwitch<KeyType>.AddSwitchCase(const name: KeyType; const value: TSwitchProc): TGenericSwitch<KeyType>;
begin
  Result := Self;
  Add(ValidateKey(Name), Value);
end;

class function TGenericSwitch<KeyType>.CaseOf(const Key: KeyType): TGenericSwitch<KeyType>;
begin
  Result := Create;
  Result.TheTargetKey := Key;
end;

function TGenericSwitch<KeyType>.ElseCase(const Action: TSwitchProc): TGenericSwitch<KeyType>;
begin
  Result := Self;
  TheElseCase := Action;
end;

procedure TGenericSwitch<KeyType>.EndCase;
var
  DoIt : TSwitchProc;
begin
  if TryGetValue(TheTargetKey, DoIt)
  then DoIt
   else
   if Assigned(TheElseCase)
    then TheElseCase;
  Destroy;
end;

procedure TGenericSwitch<KeyType>.SetTheElseCase(const Value: TSwitchProc);
begin
  FTheElseCase := Value;
end;

procedure TGenericSwitch<KeyType>.SetTheTargetKey(const Value: KeyType);
begin
  FTheTargetKey := ValidateKey(Value);
end;

function TGenericSwitch<KeyType>.ValidateKey(Key: KeyType):KeyType;
begin
  Result := Key;
end;

{ TStringSwitch }

function TStringSwitch.ValidateKey(key: String): String;
begin
  Result := LowerCase(Key);
end;


end.

Another Generics / RTTI bug. Attributes are ignored in parametrized types.

The output from the code below, shows that you cannot enumerate attributes for properties of a parametrized type such as TOpenClass.

If you close the class as a TDecidedClass = TOpenClass, any attributes declared in TDecidedClass may have enumerable attributes, but the attributes declared for properties in TOpenClass are still not enumerable.

Output from the code:

Properties for TBaseClass
Normal
Blinged [Bling]

Properties for TBaseParam
BlingTFails <- Note the lack of a [Bling] attribute here 
BlingIntFails <- Note the lack of a [Bling] attribute here 
Normal 
Blinged [Bling] 


Properties for TBaseInt 
BlingInt [Bling] 
BlingTFails <- Note the lack of a [Bling] attribute here 
BlingIntFails <- Note the lack of a [Bling] attribute here 
Normal 
Blinged [Bling]

program AttributeFailsForParametricGenericType;

{$APPTYPE CONSOLE}

uses
  ExceptionLog,
  Classes,
  Generics.Defaults,
  RTTI;

type
  Bling = class(TCustomAttribute);

  TBaseClass = class
  private
    function GetBling: Integer;
    function GetNormal: Integer;
    procedure SetBling(const Value: Integer);
    procedure SetNormal(const Value: Integer);
  public
    procedure Inspect;
    property Normal:Integer read GetNormal write SetNormal;
    [bling] property Blinged:Integer read GetBling write SetBling;
  end;

  TBaseParam = class(TBaseClass)
  private
    function GetBlingTFails: T;
    procedure SetBlingTFails(const Value: T);
    function GetBlingIntFails: Integer;
    procedure SetBlingIntFails(const Value: Integer);
  public
    [bling] property BlingTFails:T read GetBlingTFails write SetBlingTFails;
    [bling] property BlingIntFails:Integer read GetBlingIntFails write SetBlingIntFails;
  end;

  TBaseInt = class(TBaseParam)
  private
    function GetBlingInt: Integer;
    procedure SetBlingInt(const Value: Integer);
  public
    [bling] property BlingInt:Integer read GetBlingInt write SetBlingInt;
  end;


{ TBaseClass }

function TBaseClass.GetBling: Integer; begin end;
function TBaseClass.GetNormal: Integer; begin end;

procedure TBaseClass.Inspect;
var
  Context : TRttiContext;
  SourceType : TRttiType;
  SourceProp : TRttiProperty;
  SourceAttribute : TCustomAttribute;
  s : String;
begin
  Context := TRttiContext.Create;
  try
    SourceType := Context.GetType(Self.ClassType);
    Writeln('');
    Writeln(ClassName);

    for SourceProp in SourceType.GetProperties
    do begin
      s := SourceProp.Name;

      for SourceAttribute in SourceProp.GetAttributes
      do begin
        s := s + ' [' + SourceAttribute.ClassName + ']';
      end;
      Writeln(s);
    end;
  finally
    Context.Free;
  end;
end;

procedure TBaseClass.SetBling(const Value: Integer); begin end;
procedure TBaseClass.SetNormal(const Value: Integer); begin end;

{ TBaseParam }
function TBaseParam.GetBlingTFails: T; begin end;
function TBaseParam.GetBlingIntFails: Integer; begin end;
procedure TBaseParam.SetBlingTFails(const Value: T); begin end;
procedure TBaseParam.SetBlingIntFails(const Value: Integer); begin end;

{ TBaseInt }
function TBaseInt.GetBlingInt: Integer; begin end;
procedure TBaseInt.SetBlingInt(const Value: Integer); begin end;


var
  Base : TBaseClass;
  BaseT : TBaseParam;
  BaseInt : TBaseInt;
begin
  Base := TBaseClass.Create;
  Base.Inspect;

  BaseT := TBaseParam.Create;
  BaseT.Inspect;

  BaseInt := TBaseInt.Create;
  BaseInt.Inspect;

  Readln;
end.

Programming Windows Phone 7 by Charles Petzold

Microsoft are very keen to get people started on development for Windows Phone 7. So keen that they are giving away the 1013 pages thick eBook version (in PDF or XPS format) of Charles Petzold's Programming Windows Phone 7.

Now, all we need is the ability use Prism :)

EurekaLog 6.0.25 RC2 (XE compatible) available for registered users

FYI - EurekaLog offers RC2 of an XE compatible v6.0.25 of EurekaLog to registered users at their website. https://www.eurekalog.com/login.php

It installed smoothly for both D2010 and DXE, and appear to work as expected for both.

How time flies...

It is amazing how time flies when you get engaged to the woman of your dreams, and move to another city! In the midst of moving all the furniture, refurbishing and selling the old apartment, getting to know my new bonus kids, and walking the dog - I also changed jobs :) I am no longer an Oslo citizen, but mainly work from home, about 180km further south on the sunny coastline from Oslo. So... what happened on the Delphi level of things?

Status: D5 -> D2009 port: It never completed. The dependencies between the old TopView grid and the database ORM were too large, and the TopView component turned to be for all practical purposes - non-portable. Not only because of the Unicode change, but also due to the fact that they changed the database TBookmark definition. At that point, it became clear that there was not enough resources/time to complete the work needed to complete port within reasonable cost.

I did plan on writing further posts on the migration process, but the main points about the Unicode change have already been covered elsewhere. All in all, it is quite remarkable how smooth that transition seem to have gone.

In January 2010, I began in a new position at Tine SA. No more porting projects, but writing and maintaining data warehouse, production and logistics related code for the dairy product manufacturing at Tine, using Delphi 2010, and integrating with Lawson's MOVEX M3 AS/400 ERP systems, as well as various robotic systems, using MSSQL Server 2008 as the backend.

The Tine team is a distributed team, working from many different geographical locations, that meet up at the same place physically just a few days every month. I am pleasantly surprised of how enjoyable and effective this way of working is! Naturally, it requires a bit more planning and coordination, but with good project management and regular meetings - it works better than I could have hoped for. The only drawback is that when I am mentally engaged in solving a new software challenge, my lady will complain that I spend too much time by the computer :)

Generics: We recently started refactoring the class hierarchies using Generics, and that has shaved about 7% off the number of lines of code in the projects so far. Hopefully, when we are done - the codebase will be 10-15% smaller than what we started with, and a lot simpler to maintain.

Generics is fun. Generics is also somewhat painful, as there are a lot of flaws in D2010. I can't wait to see which 87 generics issues that have been fixed in Delphi XE!

During the fall, I plan resuming the work on the FDCLib, and focus on getting the most out of Generics, Attributes, and Anonymous Methods. Stay tuned.