Difference between revisions of "User:Nhollm"
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TDictionary is a generic data-container for key-value pairs (associative array). <br> | TDictionary is a generic data-container for key-value pairs (associative array). <br> | ||
− | It was introduced with Generics.Collections (rtl-generics) in FPC 3.1.1+. It's part of the FPC Runtime Library and fully Delphi compatible.<br> | + | It was introduced with Generics.Collections (rtl-generics) in FPC 3.1.1+ and published in major release 3.2 (June 2020). It's part of the FPC Runtime Library and fully Delphi compatible.<br> |
− | (Like in Delphi) The TDictionary is implemented as a hash table. This means the key-value pairs are not sorted in a defined order. (= not iterable by index??)<br> | + | (Like in Delphi) The TDictionary is implemented as a hash table. This means the key-value pairs are not sorted in a defined order. (in memory / = not iterable by index??)<br> |
− | + | Both key and value can be of primitive type (e.g. integer, string, bool..) or rather complex (e.g. classes, records, arrays) | |
− | |||
==Basic syntax (FPC)== | ==Basic syntax (FPC)== | ||
Line 73: | Line 72: | ||
WriteLn(MyDictionary.Items['Key1']); | WriteLn(MyDictionary.Items['Key1']); | ||
</syntaxhighlight> | </syntaxhighlight> | ||
− | If the provided key does not exist, this will throw an Error: 'Dictionary Key does not Exist'. You can use | + | If the provided key does not exist, this will throw an Error: 'Dictionary Key does not Exist'. You can use [[#TryGetValue|TryGetValue()]] instead. |
===Item Count=== | ===Item Count=== | ||
Line 121: | Line 120: | ||
===Trying=== | ===Trying=== | ||
These functions return a boolean.<br> | These functions return a boolean.<br> | ||
− | True if sucessfull, False if not. No error is thrown, so they are a good alternative to | + | True if sucessfull, False if not. No error is thrown, so they are a good alternative to [[#Get Value|Get Value]] or [[#Add|Add()]]. |
====TryAdd==== | ====TryAdd==== | ||
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writeln('not sucessfull'); | writeln('not sucessfull'); | ||
</syntaxhighlight> | </syntaxhighlight> | ||
− | Limitation: TryAdd does '''not''' update an existing keys value. Use AddOrSetValue() instead. (Even tho there is no feedback provided) | + | Limitation: TryAdd does '''not''' update an existing keys value. Use [[#AddOrSetValue|AddOrSetValue()]] instead. (Even tho there is no feedback provided) |
====TryGetValue==== | ====TryGetValue==== | ||
Line 160: | Line 159: | ||
You can set up custom Functions/Procedures which are triggered if an Key or Value got added/removed.<br> | You can set up custom Functions/Procedures which are triggered if an Key or Value got added/removed.<br> | ||
To do this, we add 2 procedures to the class we specialize from TDictionary.<br> | To do this, we add 2 procedures to the class we specialize from TDictionary.<br> | ||
− | The TDictionary class provides the in-build functions 'OnKeyNotify' and 'OnValueNotify'. | + | The TDictionary class provides the in-build functions 'OnKeyNotify' and 'OnValueNotify'. We assign them to our procedures. (via function pointers??)<br> |
(Hint: If you update a existing value, there is no "updated"Event. Instead "removed" followed by "added" is triggered.) | (Hint: If you update a existing value, there is no "updated"Event. Instead "removed" followed by "added" is triggered.) | ||
TODO: get the Key Name inside the ValueNotify-Event kontext | TODO: get the Key Name inside the ValueNotify-Event kontext | ||
Line 189: | Line 188: | ||
procedure TStrStrDictionary.DoValueNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification); | procedure TStrStrDictionary.DoValueNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification); | ||
begin | begin | ||
− | Writeln(AAction);//can be cnRemoved or cnAdded | + | //Writeln(AAction);//can be 'cnRemoved' or 'cnAdded' |
if AAction = cnAdded then | if AAction = cnAdded then | ||
writeln('A Value got added, the value is:', AItem) | writeln('A Value got added, the value is:', AItem) | ||
Line 219: | Line 218: | ||
</syntaxhighlight> | </syntaxhighlight> | ||
+ | |||
+ | ==Using Classes== | ||
+ | |||
+ | You can use classes for Keys and/or Values. | ||
+ | Because of the fact that all created classes must be manually freed, it is strongly recommended to use TObjectDictionary instead.<br> | ||
+ | A TObjectDictionary takes ownership of its contained classes and frees them automaticly if its freed. | ||
+ | |||
+ | <syntaxhighlight lang="pascal"> | ||
+ | {$mode objfpc} | ||
+ | program example; | ||
+ | |||
+ | uses | ||
+ | Generics.Collections; | ||
+ | |||
+ | type | ||
+ | |||
+ | TMyTestClass = class | ||
+ | Name : string; | ||
+ | end; | ||
+ | |||
+ | TIntClassDictionary = specialize TDictionary<Integer, TMyTestClass>; | ||
+ | |||
+ | var | ||
+ | MyDictionary : TIntClassDictionary; | ||
+ | i: integer; | ||
+ | MyClass : TMyTestClass; | ||
+ | begin | ||
+ | MyDictionary := TIntClassDictionary.Create; | ||
+ | try | ||
+ | for i:= 0 to 5 do | ||
+ | begin | ||
+ | MyClass := TMyTestClass.Create; | ||
+ | MyClass.Name := 'Something'; | ||
+ | MyDictionary.Add(i,MyClass); | ||
+ | end; | ||
+ | finally | ||
+ | //is this even necessary????? | ||
+ | for MyClass in MyDictionary.Values do | ||
+ | begin | ||
+ | MyClass.Free; | ||
+ | end; | ||
+ | |||
+ | MyDictionary.Free; | ||
+ | end; | ||
+ | end. | ||
+ | </syntaxhighlight> | ||
==Exceptions== | ==Exceptions== |
Latest revision as of 00:31, 16 May 2024
Warning: All of this is subject to change. Do NOT use it until its finished. For any Questions or Input write me an E-Mail nhollm@gmx.de or write me at the forums 'nhollm'.
TDictionary
TDictionary is a generic data-container for key-value pairs (associative array).
It was introduced with Generics.Collections (rtl-generics) in FPC 3.1.1+ and published in major release 3.2 (June 2020). It's part of the FPC Runtime Library and fully Delphi compatible.
(Like in Delphi) The TDictionary is implemented as a hash table. This means the key-value pairs are not sorted in a defined order. (in memory / = not iterable by index??)
Both key and value can be of primitive type (e.g. integer, string, bool..) or rather complex (e.g. classes, records, arrays)
Basic syntax (FPC)
{$mode objfpc}
program Example;
uses
Generics.Collections;
type
TStrStrDictionary = specialize TDictionary<string, string>;
var
MyDictionary : TStrStrDictionary;
begin
MyDictionary := TStrStrDictionary.Create;
try
//do stuff with your dictionary..
finally
MyDictionary.Free;
end;
end.
See also #Delphi syntax
Usage:
Add
AddOrSetValue() is recommended, because Add() will fail, if the key already exists: 'Dublicate not allowed in Dictionary'.
Add
MyDictionary.Add('Key1', 'Value1');
AddOrSetValue
recommended
MyDictionary.AddOrSetValue('Key1', 'Value1');
Remove
MyDictionary.Remove('Key2');
If the Key does not exist, no Error is thrown.
Clear
MyDictionary.Clear;
Get Value
WriteLn(MyDictionary.Items['Key1']);
If the provided key does not exist, this will throw an Error: 'Dictionary Key does not Exist'. You can use TryGetValue() instead.
Item Count
Total number of Items in dictionary (count)
WriteLn('Items in Dictionary: ', IntToStr(MyDictionary.Count));
Loops
Loop Keys
for KeyStr in MyDictionary.Keys do
WriteLn('Found key:', KeyStr);
Loop Values
for ValueStr in MyDictionary.Values do
WriteLn('Found value: ', ValueStr);
Loop Key-Value-Pairs
//var KeyValuePair : TStrStrDictionary.TDictionaryPair;
for KeyValuePair in MyDictionary do
WriteLn('Found a Pair: Key:' , KeyValuePair.Key , ' Value:' , KeyValuePair.Value);
Check If Key/Value Exists
//Check if Key exists
if MyDictionary.ContainsKey('Key1') then
WriteLn('key exists')
else
WriteLn('key not found');
//Check if Value exists
if MyDictionary.ContainsValue('Searched value') then
writeln('value exists')
else
writeln('value not found');
Trying
These functions return a boolean.
True if sucessfull, False if not. No error is thrown, so they are a good alternative to Get Value or Add().
TryAdd
if MyDictionary.TryAdd('Key','TestValue') then
writeln('added successfully')
else
writeln('not sucessfull');
Limitation: TryAdd does not update an existing keys value. Use AddOrSetValue() instead. (Even tho there is no feedback provided)
TryGetValue
TryGetValue takes two Arguments ->(key, value) and returns a boolean.
If found, it returns True and the provided 'value' variable becomes the value.
If not found, the function returns False and the provided 'value'-variable is nil.
//var SearchedValue: string;
if MyDictionary.TryGetValue('Key', SearchedValue) then
WriteLn('Key found. Its value is: ' + SearchedValue)
else
WriteLn('Could not get value');
//writeln(BoolToStr(MyDictionary.TryGetValue('Key', SearchedValue), true));
ToArray
Returns an Array of type 'TDictionaryPair'.
//var myArray : array of TStrStrDictionary.TDictionaryPair;
myArray := MyDictionary.ToArray()
//WriteLn(length(myArray));
//WriteLn(myArray[0].Key)
//WriteLn(myArray[0].Value)
Event Notifications
You can set up custom Functions/Procedures which are triggered if an Key or Value got added/removed.
To do this, we add 2 procedures to the class we specialize from TDictionary.
The TDictionary class provides the in-build functions 'OnKeyNotify' and 'OnValueNotify'. We assign them to our procedures. (via function pointers??)
(Hint: If you update a existing value, there is no "updated"Event. Instead "removed" followed by "added" is triggered.)
TODO: get the Key Name inside the ValueNotify-Event kontext
{$mode objfpc}
program Example;
uses
Generics.Collections;
type
TStrStrDictionary = Class(Specialize TDictionary<String,String>)
private
procedure DoKeyNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
procedure DoValueNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
end;
procedure TStrStrDictionary.DoKeyNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
begin
//WriteLn(AAction);//AAction can be 'cnRemoved' or 'cnAdded'
if AAction = cnAdded then
writeln('A Key got added, the Key is:', AItem)
else if AAction = cnRemoved then
writeln('A Key got removed, the Key was:', AItem)
end;
procedure TStrStrDictionary.DoValueNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
begin
//Writeln(AAction);//can be 'cnRemoved' or 'cnAdded'
if AAction = cnAdded then
writeln('A Value got added, the value is:', AItem)
else if AAction = cnRemoved then
writeln('A Value got removed, the value was:', AItem)
end;
var
MyDictionary : TStrStrDictionary;
TestArr : array of TStrStrDictionary.TDictionaryPair;
begin
MyDictionary := TStrStrDictionary.Create;
//Event notifications:
MyDictionary.OnKeyNotify:=@MyDictionary.DoKeyNotify;
MyDictionary.OnValueNotify:=@MyDictionary.DoValueNotify;
try
MyDictionary.AddOrSetValue('Key1', 'Value1');//triggers 'Add' Event
MyDictionary.AddOrSetValue('Key1', 'New Value');//triggers 'Add' and 'Remove' Event
MyDictionary.Remove('Key1');//triggers 'Remove' Event
readln();
finally
MyDictionary.Free;
end;
end.
Using Classes
You can use classes for Keys and/or Values.
Because of the fact that all created classes must be manually freed, it is strongly recommended to use TObjectDictionary instead.
A TObjectDictionary takes ownership of its contained classes and frees them automaticly if its freed.
{$mode objfpc}
program example;
uses
Generics.Collections;
type
TMyTestClass = class
Name : string;
end;
TIntClassDictionary = specialize TDictionary<Integer, TMyTestClass>;
var
MyDictionary : TIntClassDictionary;
i: integer;
MyClass : TMyTestClass;
begin
MyDictionary := TIntClassDictionary.Create;
try
for i:= 0 to 5 do
begin
MyClass := TMyTestClass.Create;
MyClass.Name := 'Something';
MyDictionary.Add(i,MyClass);
end;
finally
//is this even necessary?????
for MyClass in MyDictionary.Values do
begin
MyClass.Free;
end;
MyDictionary.Free;
end;
end.
Exceptions
To handle Exceptions, import the SysUtils Library.
{$mode objfpc}
program Example;
...
uses
... SysUtils;
try
WriteLn(MyDictionary.Items['KeyXY']); // Accessing a non-existing key
except
on E: Exception do begin
WriteLn('An exception was raised: ', E.Message);
WriteLn(E.ClassName);
end;
end;
//Output:
// An exception was raised: Dictionary key does not exist
//EListError
Delphi
{$mode delphi}
uses generics.collections;
type TStrIntDict = TDictionary<string,integer>;
var
MyDict : TStrIntDict;
begin
MyDict:=TStrIntDict.create;
MyDict.AddorSetValue('foo',42);
if MyDict.ContainsKey('foo') then
WriteLn(MyDict['foo']);
end.