Hacker News Reader

Comment by mquander | Hacker News Reader

For example, to filter an array is lovely:

  filteredArray = [allRecords filteredArrayUsingPredicate:
    [NSPredicate predicateWithFormat:@"someField == %d", someFieldFilterValue]];

A four-word name for filter and filtering for equality by using a string formatting DSL are not really on my list of lovely things. I'm sure Objective-C does something well but this guy is not pointing it out.

View on HN

Yeah, I found that line hideous - ridiculously unintuitive and hard to read compared to the equivalent in say, ruby.

Maybe the whole essay would have been better framed something like: "Objective C: not quite as bad as Java!"

Just curious, for comparison: what would the equivalent be in Ruby?

my_array.select { |item| item == somefiltervalue }

At least that's one way to do it in ruby.

    filteredArray = [allRecords filteredArrayUsingPredicate:
        [NSPredicate predicateWithFormat:@"someField == %d",   someFieldFilterValue]];

in ruby:

    all_records.select {|r| r.some_field == some_field_filter_value}

in clojure:

    (filter #(= % some-filter-value) all-records)

in haskell:

    filter (\someField -> x == someFilterValue) allRecords

Let's be fair, in Objective-C, this could be actually more like

  NSIndexSet *indicies = [allRecords indexesOfObjectsPassingTest:^ (id obj, NSUInteger idx, BOOL *stop) { return [obj someField] == someFieldFilterValue; }];
  filteredArray = [allRecords objectsAtIndexes:indicies];

rather than what the article had in mind.

EDIT: oh, someFieldFilterValue was an integer, wasn't it. Fixed.

Hard to believe anyone would use that as an example. In C# you could do:

filteredArray = allRecords.Find(i => i.someField == filterValue)

EDIT: Not sure why the downvote, I'm simply stating that many other languages have far better syntax for filtering an array so I'm not sure why the author would think the syntax in Obj-c is all that great unless they have never done the same thing in any other language.

Reply on news.ycombinator.com