Enumerate the values of an NS_ENUM using a block.

EnumerateWithBlock.m

typedef NS_ENUM(NSUInteger, ASTGem) {
    ASTGemUnknown = 0,
    ASTGemGarnet,
    ASTGemAmethyst,
    ASTGemPearl,
    ASTGemRose,
};


static NSString * const ASTGemNames[] = {
    [ASTGemUnknown]     = nil,
    [ASTGemGarnet]      = @"Garnet",
    [ASTGemAmethyst]    = @"Amethyst",
    [ASTGemPearl]       = @"Pearl",
    [ASTGemRose]        = @"Rose Quartz",
};


void EnumerateASTGemsWithBlock(void (^enumerationBlock)(ASTGem gem, NSString *name, BOOL *stop)) {
    NSUInteger count = sizeof(ASTGemNames) / sizeof(NSString *);
    for (NSUInteger idx = 0; idx < count; idx++) {
        ASTGem gem = (ASTGem)idx;
        NSString *name = ASTGemNames[gem];
        BOOL stop = NO;
        enumerationBlock(gem, name, &stop);
        if (stop) {
            break;
        }
    }
}


static NSString * NSStringFromASTGem(ASTGem gem) {
    return ASTGemNames[gem];
}


static ASTGem ASTGemFromNSString(NSString *aString) {
    aString = [aString lowercaseString];

    __block ASTGem matchingGem = ASTGemUnknown;
    EnumerateASTGemsWithBlock(^(ASTGem gem, NSString *name, BOOL *stop) {
        if ([aString isEqualToString:name]) {
            matchingGem = gem;
            *stop = YES;
        }
    });

    return matchingGem;
}