swiftfoundation

what is the keyword Protocol (capital P) do in Swift

Just found you can type Protocol directly, and its Type different from other 2 cases
enter image description here

actually you can try init it and got a error message that some kind of hint something
enter image description here

but what on earth does the Protocol do in Swift?

Solution

  • Protocol is a class which is defined in the Objective-C runtime and represents an Objective-C protocol. Example:

    let p = objc_getProtocol("NSObject")! 
print(p.dynamicType) // Output: "Protocol"

    objc_getProtocol is declared as

    /** 
 * Returns a specified protocol.
 * 
 * @param name The name of a protocol.
 * 
 * @return The protocol named \e name, or \c NULL if no protocol named \e name could be found.
 * 
 * @note This function acquires the runtime lock.
 */
@available(OSX 10.5, *)
public func objc_getProtocol(name: UnsafePointer<Int8>) -> Protocol!

    and Protocol is declared as

    // typedef Protocol is here:

// All methods of class Protocol are unavailable. 
// Use the functions in objc/runtime.h instead.

@available(OSX 10.0, *)
public class Protocol {
}

    The underlying Objective-C definitions can be found in <objc/Protocol.h> and <objc/runtime.h>.