[fpc-devel] Dnamic packages support

[Florian Klaempfl]

Michael Van Canneyt schrieb:
> 
> On Sat, 3 Nov 2007, Florian Klaempfl wrote:
> 
>> Leonardo M. Ramé schrieb:
>>> Reading a post in "public.mseide-msegui.talk", the mseide discussion
>>>  list, I found this:
>>>
>>> "Florian has committed the beginning of dynamic packages support".
>>>
>>> With "Dynamic Packages" you mean a platform independent way of
>>>  implementing something similar to
>>> .Dlls (or .bpl)? without creating each library its own memory manager?,
>>>  where objects can flow
>>> across all libraries without problems?
>>>
>> If it is finished, it would be something like this yes. However, I'am
>> not convinced of the use of dyn. loaded packages for an OSS project so I
>> played only with it.
> 
> Hm. I don't see what OSS or not OSS has to do with it ?

Packages have major drawbacks
- DLL/shared lib hell; remember each fpc build gets/needs it's own set
of packages
- memory footprint of programs increase significantly since no
smartlinking is possible, I created once a pure shared linked lazarus:
it depended on 50 MB of shared libs.
- speed of programs decreases by ~10% because each global variable
access gets indirect (like pic)
- major blow up of installer size

> 
> Packages are IMHO a pre-requisite for any good plugin system.
> It allows you to enable/disable certain features of a program based on the 
> particular system you install the package on, without having to recompile
> your complete application for this particular system.

Then it's the task of a programmer to design a proper plugin interface.
A plugin interface based on packages (in the delphi sense) requires that
the main program and the plugin use exactly the same compiler and rtl.

> 
> Lazarus is an IDE and therefore recompilation is IMHO an acceptable solution,
> since the person using it is a developer (even so, this would be too much asked
> for most devels in my company) but the same cannot be said for most end-user 
> applications, OSS or not. For example, I don't think we can expect an end 
> user to recompile XMMS if he decides to use ogg vorbis files instead of .mp3...
> 
> Apart from the recompilation issue, packages allow you to have type-safety in 
> plugins. A normal dll does not offer this (which is why techniques such as 
> COM are used on Windows). I could not build my day-time job application if 
> packages did not exist...
> 
> So I do think packages are really a must; I lack the skill to implement them
> in the compiler, but will be glad to assist in any design issues or even 
> creating any RTL code that you would need, if this is the problem for you.

I see only a real use of packages if one doesn't want to distribute the
source of the IDE like Delphi.