Migrating to Obj-C Literals - Jeremy W. Sherman

Obj-C literals make your code cleaner and more compact, but hand-updating a large codebase to take advantage of Obj-C literals would be a bore, and all too easy to mess up during a distracted moment.

This is what automated refactoring tools were designed for. And Apple has provided us with an oft-overlooked arrow in our devtools quiver that’s just what we need here: tops.

Check out man tops. The tool has a decent understanding of Obj-C syntax and accepts scripts that let you rewrite code to use new method calls, new functions, and what-have-you. The examples make it look like this tool was invented to ease the transition from NeXT-style Obj-C to Cocoa, like this gem:

replace "NXGetNamedObject(<b args>)" with same
    error "ApplicationConversion: NXGetNamedObject() is obsolete.
           Replace with nib file outlets."

That should take some of you way back.

Anyway, with this tool, modernizing your code can be as simple as:

tops -semiverbose -scriptfile literals.tops **/*.(h|m|hpp|mm)

Want to check that it will do the right thing? Throw -dont into the args.

Want to watch over its shoulders as it rewrites your code? Replace -semiverbose with straight-up -verbose.

Now, for that magical script file:

/*tops -semiverbose -scriptfile literals.tops Project/**/*.{h,m,hh,mm}*/ /* @file literals.tops * @author Jeremy W. Sherman * @url http://jeremywsherman.com/ * @date 2012-08-27 */ /* Dictionary Creation * Literals create immutable dicts, so only replace NSDictionary not * NSMutableDictionary. */ replace "[NSDictionary dictionary]" with "@{}" replace "[[NSDictionary alloc] init]" with "@{}" replace "[NSDictionary new]" with "@{}" replace "[NSDictionary dictionaryWithObjectsAndKeys:<a args>]" with "@{<args>}" within ("<args>") { replace ", nil" with "" replace ", ()nil" with "" replace "<val>, <key>" with "<key> : <val>!!!" replace "!!!" with "" } replace "[[NSDictionary alloc] initWithObjectsAndKeys:<a args>]" with "@{<args>}" within ("<args>") { replace ", nil" with "" replace ", ()nil" with "" replace "<val>, <key>" with "<key> : <val>!!!" replace "!!!" with "" } /* Dictionary Access */ /* We distinguish between simple tokens and entire expressions, and wrap * expressions with parens in the substitution. * We do the same for arrays later. */ replace "[<t dict> objectForKey:<key>]" with "<dict>[<key>]" replace "[<expr> objectForKey:<key>]" with "(<expr>)[<key>]" /* Dictionary Mutation */ replace "[<t dict> setObject:<obj> forKey:<key>]" with "<dict>[<key>] = <obj>" replace "[<expr> setObject:<obj> forKey:<key>]" with "(<expr>)[<key>] = <obj>" /* Array Creation */ replace "[NSArray array]" with "@()" replace "[[NSArray alloc] init]" with "@()" replace "[NSArray new]" with "@()" replace "[[NSArray alloc] initWithObjects:<a objs>]" with "@(<objs>)" within ("<objs>") { replace ", nil" with "" replace ", ()nil" with "" } replace "[NSArray arrayWithObjects:<a objs>]" with "@(<objs>)" within ("<objs>") { replace ", nil" with "" replace ", ()nil" with "" } /* Array Access */ replace "[<t arr> objectAtIndex:]" with "<arr>[]" replace "[<expr> objectAtIndex:]" with "(<expr>)[]" /* Array Mutation */ replace "[<t arr> replaceObjectAtIndex: withObject:<obj>]" with "<arr>[] = <obj>" replace "[<expr> replaceObjectAtIndex: withObject:<obj>]" with "(expr)[] = <obj>" /* Number Literals */ /* Not handled, because Apple releases don't yet support boxed expressions, * many numbers are likely to be created with boxed expressions, and tops * can't distinguish type well enough to restrict transformations to * those involving only numeric literals. */

And here’s an Obj-C file to test it against:

// clang -g -Weverything -framework Foundation literals.m -o literals /* @file literals.m * @author Jeremy W. Sherman * @url http://jeremywsherman.com/ * @date 2012-08-27 */ #import <Foundation/Foundation.h> int main(void) { @autoreleasepool { NSString *string = @"string"; /* Array Literals */ NSArray *array = [[NSArray alloc] init]; array = [NSArray array]; array = [[NSArray alloc] initWithObjects:@"0", @"1", @"2", (void *)nil]; array = [NSArray arrayWithObjects:@"0", @"1", @"2", nil]; /* Don't rewrite mutable creation, since container literals * create immutable containers. */ NSMutableArray *marray = [NSMutableArray arrayWithObjects:@"NO", nil]; [marray replaceObjectAtIndex:0 withObject:string]; string = [array objectAtIndex:0]; array = [[NSMutableArray alloc] initWithObjects: @"1", @"2", @"3", nil]; /* Dictionary Literals */ NSDictionary *dict = [[NSDictionary alloc] init]; dict = [NSDictionary dictionary]; dict = [[NSDictionary alloc] initWithObjectsAndKeys:@"obj", @"key", @"v", @"k", (void *)nil]; dict = [NSDictionary dictionaryWithObjectsAndKeys: @"bar", @"key", (void *)nil]; NSMutableDictionary *mdict = [[NSMutableDictionary alloc] init]; [mdict setObject:@"foo" forKey:@"key"]; /* Trickier? */ NSArray *arrays[] = {array, array}; id obj = [*arrays objectAtIndex:0]; obj = [*(arrays + 1) objectAtIndex:0]; NSLog(@"%@", obj); } }