In stringlist can we get addorset method

[Packs]

In tstringlist can we add new method addorset

[cdbc]

Hi
What do you mean, what would that do, how should it look...?!?
If You show me, I can rather quickly add it to my "IStringList" implementation, which btw. is found here.
Regards Benny

[Zvoni]

In tstringlist can we add new method addorset

Class Helper?
Derived Class?

[Thaddy]

[editted version, covers more cases]
Yes, something like this (untested):

Code: Pascal  [Select][+][-]

1. {$mode objfpc}{$modeswitch typehelpers}{$H+}
2. uses classes;
3.  
4. type
5.   TAddOrSet = type helper for Tstringlist
6.   function AddOrSet(const value:string;obj:TObject = nil):integer;inline;
7.   function AddOrSet(const name,value:string; obj:TObject = nil):integer;inline;
8.   end;
9.  
10.   function TAddOrSet.AddOrSet(const value:string;obj:TObject):integer;
11.   begin
12.     Result:= self.indexof(value);
13.     if result = -1 then
14.       result:=self.addobject(value,obj)
15.     else
16.     begin
17.       self[result]:= value;
18.       self.objects[result]:=obj;
19.     end;
20.   end;
21.  
22.   function TAddOrSet.AddOrSet(const name,value:string;obj:TObject):integer;inline;
23.   begin
24.     Result:= self.indexof(name);
25.     if result = -1 then
26.     begin
27.       self.addpair(name,value,obj);
28.       result := self.indexof(name);
29.     end
30.     else
31.     begin
32.       self.values[name]:= value;
33.       self.objects[result] := obj;
34.     end;
35.   end;
36.  
37. begin
38. end.

[Packs]

@taddy

Thank you 🙏

[Thaddy]

I just posted a better version, editted my post. Covers more cases.

[egsuh]

If you set TStringList.Sorted = true and TStringList.Duplicates = dupIgnore then it will do what we guess you want to achieve.

https://www.freepascal.org/docs-html/rtl/classes/tstringlist.add.html

Or if you want to set value for a name, e.g. Name=Value format, than simply

  Values [name] := newvalue;

does it.

[Thaddy]

Nope. For both cases.
If you want to do it properly and without relying on sorted, the type helper I showed is a better option.
It does not make any assumption about options.
The latter suggestion is plain wrong because the item may not exist.
(Look how I handle addpair with object)

Note my code is not fast, I intentionally chose the most universal cases.
comparing the value and obj parts is really overkill, so even if value and obj are equal these will be overwritten anyway.

[silvercoder70]

dumb question ... if you happen to call this "add or set" with the same key value but different objects, or keeps a list in sync with database, what happens to the existing element that might be already stored. For example:

initially...

list.AddOrSet(serial-number, object-associated-with-serial-number);

on loading from dataset (say 10 minutes later)...

list.AddOrSet(serial-number, object-associated-with-serial-number-updated);

what happens with the object associated with serial-number initially?

[Thaddy]

If objects are equal, that means they are the same object instance, hence no need to take provisions for that...
You did not consider that, did you? It is a pointer comparison, the reference is stored.
And so it does not hurt to overwrite same valued pointers. Overwrite a pointer is likely also faster than introducing extra branching.
This is also the way the separate methods work already.

In general AddOrSet is quite a common pattern and is supported by most generics libraries for fpc.

[jamie]

TFPGMap has what is needed already.

[Packs]

TFPGMap this is third party library or it stand library

[Thaddy]

It is standard: it is in the fgl unit which is part of the rtl, it is not a separate package.
Note that it does not support everything, though: name-value pairs + objects are afaik not supported.
But if you don't need that it is a good option. It is also lightweight. Other generics libraries also supports what you want in that case.

[Thaddy]

TFPGMap has what is needed already.

Nope.
addpair(name,value,obj);
is not covered in TFpgMap. It is a strict map.
But in the simple cases it would be enough.

[cdbc]

Hi Thaddy
Nice code, do you mind if I use it in 'IStringlist'?
With credits Ofc. 
Regards Benny