a few NSDateFormatter helpers for Objective-C

NSDate+Formatters.h

/* f@s2n.io */
// DateFormat Reference : http://www.unicode.org/reports/tr35/tr35-25.html#Date_Format_Patterns

#import <Foundation/Foundation.h>

extern NSString* const DATEFORMAT_RFC3339;

@interface NSDate (FMDateFormatters)

+ (NSDate*)dateWithString:(NSString*)dateString format:(NSString*)format locale:(NSLocale*)locale timezone:(NSTimeZone*)zone;
+ (NSDate*)dateWithString:(NSString*)dateString format:(NSString*)format;
+ (NSDate*)dateWithPosixString:(NSString*)dateString format:(NSString*)format;

- (NSString*)formattedString:(NSString*)format withTimeZone:(NSTimeZone*)zone locale:(NSLocale*)locale;
- (NSString*)formattedString:(NSString*)format withTimeZone:(NSTimeZone*)zone;
- (NSString*)formattedString:(NSString*)format withOptions:(void(^)(NSDateFormatter* formatter))optionsBlock;
- (NSString*)formattedString:(NSString*)format;

- (NSString*)posixFormattedString:(NSString*)format withTimeZone:(NSTimeZone*)zone;
- (NSString*)posixFormattedString:(NSString*)format;

@end

NSDate+Formatters.m

/* f@s2n.io */

#import "NSDate+Formatters.h"

NSString* const DATEFORMAT_RFC3339 = @"yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'";

@implementation NSDate (FMDateFormatters)

- (NSString*)formattedString:(NSString*)format withTimeZone:(NSTimeZone*)zone locale:(NSLocale*)locale {
	NSDateFormatter *formatter = NSDateFormatter.new.autorelease;
	if (locale)
		formatter.locale = locale;
	formatter.dateFormat = format;
	if (zone)
		formatter.timeZone = zone;
	return [formatter stringFromDate:self];
}
- (NSString*)formattedString:(NSString*)format withTimeZone:(NSTimeZone*)zone {
	return [self formattedString:format withTimeZone:zone locale:NSLocale.currentLocale];
}
- (NSString*)formattedString:(NSString*)format withOptions:(void(^)(NSDateFormatter* formatter))optionsBlock {
	__block NSDateFormatter *formatter = NSDateFormatter.new.autorelease;
	[formatter setDateFormat:format];
	optionsBlock(formatter);
	return [formatter stringFromDate:self];
}
+ (NSTimeZone*)posixTimeZone {
	return [NSTimeZone timeZoneForSecondsFromGMT:0];
}
- (NSString*)formattedString:(NSString*)format {
	return [self formattedString:format withTimeZone:nil locale:NSLocale.currentLocale];
}
- (NSString*)posixFormattedString:(NSString*)format withTimeZone:(NSTimeZone*)zone {
	NSLocale* posixLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"].autorelease;
	return [self formattedString:format withTimeZone:zone locale:posixLocale];
}
- (NSString*)posixFormattedString:(NSString*)format {
	NSLocale* posixLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"].autorelease;
	return [self formattedString:format withTimeZone:self.class.posixTimeZone locale:posixLocale];
}
+ (NSDate*)dateWithString:(NSString*)dateString format:(NSString*)format {
	return [self dateWithString:dateString format:format locale:NSLocale.currentLocale timezone:nil];
}
+ (NSDate*)dateWithPosixString:(NSString*)dateString format:(NSString*)format {
	return [self dateWithString:dateString
						 format:format
						 locale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"].autorelease
					   timezone:self.class.posixTimeZone];
}
+ (NSDate*)dateWithString:(NSString*)dateString format:(NSString*)format locale:(NSLocale*)locale timezone:(NSTimeZone*)zone {
	if (!dateString || !format) return nil;
	NSDateFormatter *formatter = NSDateFormatter.new.autorelease;
	if (locale)
		formatter.locale = locale;
	formatter.dateFormat = format;
	if (zone)
		formatter.timeZone = zone;
	return [formatter dateFromString:dateString];
}

@end