[gmpi] Re: low level API - Abstract Factory summary
- From: Tim Hockin <thockin@xxxxxxxxxx>
- To: gmpi@xxxxxxxxxxxxx
- Date: Mon, 7 Feb 2005 16:03:32 -0800
On Tue, Feb 08, 2005 at 08:46:21AM +1300, Jeff McClintock wrote:
> struct gmpi_descriptor
> {
> char *unique_identifier;
> char *name;
> //etc
> };
For the sake of consistency, let's (for now, more on this later) name
everything consistently. GMPI_Foo. GMPI_Bar. struct GMPI_Thing. The
names may well change, but for now, let's just say that
structs/classes/typedefs all start with "GMPI" and a capital letter.
> let's call it:
>
> class GMPI_Plugin_Factory
> {
> void GetMetaData( int index, gmpi_descriptor *gd );
> GMPI_Plugin *Instantiate( int index );
> };
>
Whoah. I'd really rather not talk about how the C++ tastes until we
know how the C tastes. I was about to propose the analog in real C,
when I had a question. Why do we need this factory class. Is it really
any cleaner than having the instantiate() be a method of
struct GMPI_Descriptor ?
I'd rather see the flow be simpler:
load dll
find symbol GMPI_Descriptor()
loop for each i until GMPI_Descriptor(i) == NULL
> ..So the dll has a single exported function..
>
> extern "C" {
> __declspec (dllexport)
__declspec is not C. I don't know what it does, but it sure isn't C.
Anything like this that is not straight C needs to be thoroughly
encapsulated. Sigh.
> IGMPI_Plugin_Factory *GetPluginFactory(void)
> {
> static GMPI_Plugin_Factory factory;
> return &factory;
> }
Please make sure that *ALL* GMPI symbols that are visible are prefixed
with "GMPI". I won't argue about UglyBumpyCaps vs nice_underscores yet,
more later.
> GMPI_Plugin's 'interface' is defined as a pure abstract base class.
> This is all the host ever 'sees' to hide the internal details..
>
> class IGMPI_Plugin
> {
> virtual void placeholder1(void) = 0;
> virtual void placeholder2(void) = 0;
> };
Again, C first. Also, why "IGMPI_Plugin"? what does the leading "I"
mean? Is this some convention I just don't know?
extern "C" {
struct GMPI_Descriptor {
char *unique_identifier;
char *name;
struct GMPI_Plugin *instantiate(void);
//...
};
struct GMPI_Plugin {
//...
};
typedef struct GMPI_Descriptor *(*GMPI_Descriptor_Func)(int index);
}
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