Why can the Objective-C class and protocol have the same name, but Swift cannot, what is the difference in language implementation?

Question

Swift, Can not compile, the compiler will report an error directly.

protocol Test {}

struct Test {}


// Swift compile output:

// Untitled.swift:4:8: error: invalid redeclaration of 'Test' struct Test {}

// Untitled.swift:2:10: note: 'Test' previously declared here protocol Test {}

Objective-C, can be compiled successfully, for example NSObject is the name of the class, it is also the name of the protocol

#import <Foundation/Foundation.h>

@protocol Test
@end

@interface Test
@end

int main(int argc, char *argv[]) {
    @autoreleasepool {
        NSLog(@"Hello word");
    }
}
// Objective-C output
// 2018-03-11 23:14:20.341 Untitled[34921:1272761] Hello word

Answer 1

Objective-C and Swift have different name resolution schemes that cause this.

• Objective-C , , . ( , , , .) - . , - : Foo Foo, Foo - @protocol(Foo). .
• Swift, , . , , Foo Foo, .

, - , Swift, enum s/struct s/class es , , ; Swift, . , , , struct Test protocol Test : <name-of-your-module>.Test

, struct Test protocol Test , , . ,

struct ExpressibleByStringLiteral {}

, , . ExpressibleByStringLiteral , , stdlib, Swift.ExpressibleByStringLiteral:

struct ExpressibleByStringLiteral {}
struct S1 : ExpressibleByStringLiteral {} // error: inheritance from non-protocol type 'ExpressibleByStringLiteral'

struct S2 : Swift.ExpressiblyByStringLiteral {} // need to add methods to satisfy the protocol

Swift. , .