CODEWITHSUNDEEP
objective-cperformance
Sjakelien
Sjakelien

Reputation: 2317

coding efficiency vs execution efficiency

So I have these two methods:

-(void)importEvents:(NSArray*)allEvents {
    NSMutableDictionary *subjectAssociation = [[NSMutableDictionary alloc] init];

    for (id thisEvent in allEvents) {
        if (classHour.SubjectShort && classHour.Subject) {
            [subjectAssociation setObject: classHour.Subject forKey:classHour.SubjectShort];
        }
    }

    [self storeSubjects:subjectAssociation];
}

-(void)storeSubjects:(NSMutableDictionary*)subjects {
    NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDir  = [documentPaths objectAtIndex:0];
    NSString *subjectsList = [documentsDir stringByAppendingPathComponent:@"Subjects.plist"];

    [subjects writeToFile:subjectsList atomically:YES];
}

The first loops through an array of let's say 100 items, and builds a NSMutableDictionary of about 10 unique key/value pairs.

The second method writes this dictionary to a file for reference elsewhere in my app.

The first method is called quite often, and so is the second. However, I know, that once the dictionary is built and saved, its contents won't ever change, no matter how often I call these methods, since the number of possible values is just limited.

Question: given the fact that the second method essentially needs to be executed only once, should I add some lines that check if the file already exists, essentially adding code that needs to be executed, or can I just leave it as is, overwriting an existing file over and over again?

Should I care? I should add that I don't seem to suffer from any performance issues, so this is more of a philosophical/hygienic question.

thanks

Upvotes: 0

Views: 52

Answers (2)

gnasher729
gnasher729

Reputation: 52538

Your solution is totally over engineered, and has tons of potential to go wrong. What if the users drive is full? Does this file get backed up? Does it need backing up / are you wasting the users time backing it up? Can this fail? Are you handling it? You are concentrating on the entering and storing of data, you should be focusing on accessing that data.

I'd have a readwrite property allEvents and a property eventAssociations, declared readonly in the interface, but readwrite in the implementation file.

The allEvents setter stores allEvents and sets _eventAssociations to nil. The eventAssociations getter checks whether _eventAssociations is nil and recalculates it when needed. A simple and bullet-proof pattern.

Upvotes: 0

Warren Burton
Warren Burton

Reputation: 17382

It depends.

You say

once the dictionary is built and saved, its contents won't ever change

until they do :-)

If your app is not suffering from any performance issues on this particular loop I wouldn't try to cache for the reason that unless you somehow remember that you have a once-only write on the file you are storing up a bug for later.

This could be mitigated by using an intention revealing name on the method. i.e

-(void)storeSubjectsOnceOnlyPerLaunch:(NSDictionary*)subjects

If I got my time back for tracing down bugs caused by caching, I would have several days back in my life.

Upvotes: 1

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