SPMySQLArrayAdditions.h

//
//  SPMySQLArrayAdditions.h
//  SPMySQLFramework
//
//  Created by Rowan Beentje (rowan.beent.je) on February 23, 2012
//  Copyright (c) 2012 Rowan Beentje. All rights reserved.
//
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//  copies of the Software, and to permit persons to whom the
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//
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//  More info at <https://github.com/sequelpro/sequelpro>

/**
 * Set up a static function to allow fast mutable array insertion using
 * cached selectors.
 * At least in 10.7, inserting items into an array at a known point
 * using NSMutableArray methods appears to be the fastest way of adding
 * items to a CF/NSMutableArray.
 */
static inline void SPMySQLMutableArrayInsertObject(NSMutableArray *self, id anObject, NSUInteger anIndex)
{
	/* A note on CFArrayInsertValueAtIndex():
	 *
	 * This function here does look similar to the CF function, however that is not neccesarily the
	 * case from a performance standpoint.
	 *
	 * CFArrayInsertValueAtIndex() is mostly a wrapper around either
	 * - _CFArrayReplaceValues(obj, …) *or*
	 * - objc_msgSend(obj, @selector(insertObject:atIndex:), …)
	 *
	 * The first case would be fast, but it will only be used if the object is a native CFArrayRef, not
	 * a toll-free bridged object. In our case however, we always pass in some object of the NSMutableArray cluster,
	 * so we would always end up in the slowest path (uncached objc method invocation).
	 *
	 * Determing the performance of the objc method is more difficult, because there are multiple implementations
	 * of NSMutableArray and the "real" -[NSMutableArray insertObject:atIndex:] (located in CoreFoundation.framework)
	 * is only an abstract stub that will raise an exception if called.
	 *
	 * NSCFArray's (for CFArrays bridged to objc) implementation will wind up in _CFArrayReplaceValues().
	 * __NSArrayM's (for +[NSMutableArray array]) implementation is completely independent from the aforementioned ones.
	 */
	typedef id (*SPMySQLMutableArrayInsertObjectPtr)(NSMutableArray*, SEL, id, NSUInteger);
	static SPMySQLMutableArrayInsertObjectPtr cachedMethodPointer;
	static SEL cachedSelector;

	if (!cachedSelector) cachedSelector = @selector(insertObject:atIndex:);
	if (!cachedMethodPointer) cachedMethodPointer = (SPMySQLMutableArrayInsertObjectPtr)[self methodForSelector:cachedSelector];

	cachedMethodPointer(self, cachedSelector, anObject, anIndex);
}