README.md

Type inference in Objective-C

This project includes several macros and class categories that provide hints for compiler type inference. From simple let and var that are inspired by Swift, to foreach () {} construct that replaces for (in) {} loops.

Without type inference, the types are error-prone:

NSString *name = @"Martin";
NSMutableString *mutableName = [name mutableCopy];

NSArray<NSString *> *letters = @[@"A", @"B", @"C"];
NSMutableArray<NSString *> *mutableLetters = [letters mutableCopy];

for (NSString *letter in letters) {
    //...
}

• Types of almost all variables are not checked by compiler.
• Methods -mutableCopy discard types, because they return id.
• Array literal doesn’t check for mixed types and doesn’t propagate element type.
• Loop for (in) {} ignores element type of enumerated collection.

With type inference, this is still pure Objective-C:

let name = @"Martin";
var mutableName = [name mutableCopy];

let letters = NSArray(@"A", @"B", @"C");
var mutableLetters = [letters mutableCopy];

foreach (letter, letters) {
    //...
}

• Types of all variables are inferred from context.
• Methods -mutableCopy are redeclared with proper return type.
• Macro NSArray(…) doesn’t accept mixed types as arguments and returns NSArray with proper element type.
• Macro foreach () {} infers type of the variable from the enumerated collection.