Objective-C literals for NSDictionary, NSArray, and NSNumber

Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by openbear on Sunday February 19, 2012 @01:59PM (#3610022)

I'm glad to see these additions, but the syntax for an NSArray literal bugs me.

When I want an array literal in C, I'd write ...

  int foo[] = { 1, 2, 3, 4, 5};

... but in Objective-C, for an NSArray literal I'd write ...

  NSArray *bar = @[o1, o2, o3];

Why did they choose '[' over '{'? Oddly enough, NSDictionary uses '{'.

I feel like the syntax for an NSString literal is more natural (as a C developer).

  NSString *baz = @"look, an NSString literal";
  char szBaz[] = "look, a C string literal";

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by __david__ on Sunday February 19, 2012 @06:00PM (#3610684)

Because presumably (I don't have the new XCode to check) you can do things like:

    [someObject dictArg:@{ a:@"B" } arrayArg:@[1,2,34]];

So if they were both using "{" to set them off the parser doesn't know which one you mean until it hits the first ":" (and it can't guess from the type when the type is "id"). Now that's not impossible to write a parser that looks ahead to figure out what you mean, but it's much easier to parse if they have completely different syntax from the outset. And the "{" vs "[" distinction is very standard amongst the higher level languages, even if it isn't in straight C.

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by bebop on Sunday February 19, 2012 @03:59PM (#3610387)

I think they chose the [] for arrays and {} for dictionaries as that is the style that seems to be most popular right now. Python for instance uses this.

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by openbear on Sunday February 19, 2012 @11:56PM (#3611351)

When adding features to something, I tend to be a big fan of "when in Rome"[1]. If these were extensions to Python (or Ruby or JavaScript) then I would totally be for using '[' with arrays. As a C guy though, I would rather have seen them use '{' for NSArray and '[' for NSDictionary. Regardless, I'm glad to see this stuff added.

[1] http://en.wiktionary.org/wiki/when_in_Rome,_do_as_the_Romans...

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by xsmasher on Monday February 20, 2012 @02:10AM (#3611617)

It's already custom in objc to use {} for dicts and [] for arrays when printing them out, unless I'm misremembering. It also matches the use of those characters in JSON, so it seems natural to me.

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by __david__ on Sunday February 19, 2012 @05:50PM (#3610665)

And Perl. And Javascript. And Ruby. There's lots of precedent.

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by icodestuff on Sunday February 19, 2012 @05:23PM (#3610613)

Could be in case they want to do literal NSValues later. Since {}-syntax is used in C for both array literals and struct literals, they needed to change one, and the picked the more common one. Otherwise is foo in:

id foo = @{ @2, @5 };

an NSArray containing two NSNumbers, or an NSValue containing a struct with two pointers (which happen to be NSNumber *s)?

I'd guess there were other edge cases they didn't want to deal with, so they didn't do literal NSValues for this release.

Or it could be that it's because []-style arrays are popular these days.

Or some of both; in picking which {} to change to @[], they reasoned that lots of people have experience with []-style arrays.

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by ary on Sunday February 19, 2012 @02:07PM (#3610057)

> Why did they choose '[' over '{'? Oddly enough, NSDictionary uses '{'.

Who knows, but it seems to mirror Python in that respect. Being a fan of Python I can only approve.

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by 2mur on Sunday February 19, 2012 @02:42PM (#3610144)

Completely agree. Looks natural to me as a python/javascript guy

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Re:Objective-C literals for NSDictionary, NSArray, and NSNumber by mayoff on Sunday February 19, 2012 @04:33PM (#3610485)

Perhaps they choose @[ for arrays because it requires less lookahead than figuring out whether @{ is the start of a dictionary or an array.

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