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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for May 16th, 2018

Delphi Mqtt Clients

Posted by jpluimers on 2018/05/16

For my link archive via: [WayBack] Delphi Mqtt Client (Use Indy)https://github.com/wizinfantry/delphi-mqtt-client – 오대우 – Google+

Background reading:

–jeroen

Posted in Delphi, Development, Software Development | 10 Comments »

Delphi: a pattern for a generic factory, this one for components, but can be uses for anything having a base class like a TThread descendant.

Posted by jpluimers on 2018/05/16

Generics and constraints in Delphi is still a bit of pain.

A while ago, I needed a factory for threads. It was more convoluted than I meant it to be, so I had a short chat with Stefan Glienke.

He came up with an example similar to the one below. I tore it apart so you can on each line see what the compiler dislikes.

This fails, but was kind of how I wanted it to be:

type
   TFactory = record
     class function Manufacture<T: TBaseClass, constructor>(parameter definitions): T;
   end;

class function Manufacture<T: TBaseClass, constructor>(parameter definitions): T;
begin
  Result := T.Create(parameter values);
end;

Which means I need to update Delphi Constraints in Generics – RAD Studio XE documentation wiki

The factory:

type
  TComponentFactory = class
    class function CreateComponent<T: TComponent>(AOwner: TComponent): T; static;
  end;

class function TComponentFactory.CreateComponent<T>(AOwner: TComponent): T;
var
  ComponentClass: TComponentClass;
  Component: TComponent;
begin
  ComponentClass := T;
  Component := ComponentClass.Create(AOwner); // you can't do `T.Create(AOwner)`
  Result := T(Component); // you can't do `Result := ComponentClass.Create(AOwner);`
end;

The usage:

var
  Component: TButton;
  Owner: TComponent;
begin
  Owner := Application.MainForm;
  Component := TComponentFactory<TButton>.CreateComponent(Owner);
  Component.Parent := Owner;
end;

Full source example is at: After a discussion with Stefan Glienke: a pattern for a factory, this one for components, but can be uses for anything having a base class like a TThread descendant.

In the mean time, Spring4D has added the [Archive.is] Spring4D: TActivator record with many CreateInstance methods that allow you to create instances of classes for which you just have type information.

–jeroen

This fails:

type
   TFactory = record
     class function Manufacture<T: TBaseClass, constructor>(parameter definitions): T;
   end;

class function Manufacture<T: TBaseClass, constructor>(parameter definitions): T;
begin
  Result := T.Create(parameter values);
end;

view raw

readme.md

hosted with ❤ by GitHub


type
TComponentFactory = class
class function CreateComponent<T: TComponent>(AOwner: TComponent): T; static;
end;
class function TComponentFactory.CreateComponent<T>(AOwner: TComponent): T;
var
ComponentClass: TComponentClass;
Component: TComponent;
begin
ComponentClass := T;
Component := ComponentClass.Create(AOwner); // you can't do `T.Create(AOwner)`
Result := T(Component); // you can't do `Result := ComponentClass.Create(AOwner);`
end;

view raw

ComponentFactoryUnit.pas

hosted with ❤ by GitHub


var
Component: TButton;
Owner: TComponent;
begin
Owner := Application.MainForm;
Component := TComponentFactory<TButton>.CreateComponent(Owner);
Component.Parent := Owner;
end;

view raw

ComponentFactoryUsageUnit.pas

hosted with ❤ by GitHub

Posted in Conference Topics, Conferences, Delphi, Development, Event, Software Development | Leave a Comment »

 
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