[Biococoa-dev] Factories

Koen van der Drift kvddrift at earthlink.net
Sat Aug 28 19:31:11 EDT 2004


Still thinking about the best way to implement a flyweight pattern to 
create symbols. I finally think I understand how this works and made a 
new class called BCAminoAcidFactory. Here's its implementation:

#import "BCAminoAcidFactory.h"

static NSMutableDictionary  *aminoAcidDictionary;

@implementation BCAminoAcidFactory

- ( BCAminoAcid *)aminoAcidWithSymbol: (unichar) aSymbol
	BCAminoAcid *aminoAcid = nil;
	NSString	*symbolString = [NSString stringWithCharacters: &aSymbol 
length: 1];
	if ( aminoAcidDictionary == nil )
		aminoAcidDictionary = [[NSMutableDictionary alloc] init];
	aminoAcid = [aminoAcidDictionary objectForKey: symbolString];
	if ( aminoAcid == nil )
		aminoAcid = [[BCAminoAcid alloc] initWithSymbol: aSymbol];
		[aminoAcidDictionary setObject: aminoAcid forKey: symbolString];
	return aminoAcid;

This is in turn called by any object that needs an amino acid. So 
initWithSymbol is never called directly, alwayd through the factory 
object. If the aa already exists, it will return the one that's in the 
static dictionary, otherwise it'll create a new one.

Let me know what you think, and if I overlooked something critical. 
I'll wait for comments before committing it to CVS.

- Koen.

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