Begin forwarded message:
> From: Maxthon Chan <xcvi...@me.com>
> Subject: Re: Protocols and the +initialize class method
> Date: August 23, 2013 at 23:30:19 GMT+8
> To: Fritz Anderson <anderson.fr...@gmail.com>
>
> Well you can category on NSObject to perform the checking.
>
> Sent from my iPhone
>
>> On 2013年8月23日, at 21:28, Fritz Anderson <anderson.fr...@gmail.com> wrote:
>>
>>> On 23 Aug 2013, at 4:49 AM, Kevin Meaney <k...@yvs.eu.com> wrote:
>>>
>>> I have a protocol where I would like to include the class method
>>> +(void)initialize as being required. This way all classes that conform to
>>> the protocol have to implement initialize as part of the protocol. I
>>> suppose I'm wondering if anyone perceives any problem with doing this?
>>>
>>> For example, will including +initialize as a required protocol method
>>> interfere with objective-c automatically calling the initialize method
>>> before the class is used for the first at runtime.
>>
>> The threshold question is whether the compiler will enforce the protocol as
>> you wish. This is easy to test. The following code passes analysis and runs
>> with no problem:
>>
>> -----
>> #import <Foundation/Foundation.h>
>>
>> @protocol NeedsInitialize <NSObject>
>>
>> + (void) initialize;
>> - (void) mandatoryInstance: (NSString *) str;
>>
>> @end
>>
>> @interface NAImplementor : NSObject <NeedsInitialize>
>>
>> - (NSInteger) anotherMethod;
>>
>> @end
>>
>> @implementation NAImplementor
>>
>> - (void) mandatoryInstance:(NSString *)str
>> {
>> NSLog(@"%s gets string %@", __PRETTY_FUNCTION__, str);
>> }
>>
>> - (NSInteger) anotherMethod
>> {
>> NSLog(@"%s sending -mandatoryInstance:", __PRETTY_FUNCTION__);
>> [self mandatoryInstance: @"NAImplementor sends mandatory"];
>> return 12;
>> }
>>
>> @end
>>
>> int main(int argc, const char * argv[])
>> {
>> @autoreleasepool {
>> NAImplementor * instance = [[NAImplementor alloc] init];
>> NSLog(@"%s implementor returns %li", __PRETTY_FUNCTION__,
>> (long)[instance anotherMethod]);
>> }
>> return 0;
>> }
>> -----
>>
>> As I understand it, you want to require NAImplementor to have
>> +[NAImplementor initialize]. This code passes without this happening. It
>> seems NSObject implements +initialize, which is good enough to satisfy the
>> protocol.
>>
>> "Incomplete Objective-C Protocols," GCC_WARN_ALLOW_INCOMPLETE_PROTOCOL (Warn
>> if methods required by a protocol are not implemented in the class adopting
>> it. Only applies to Objective-C.), which is the closest warning I can find
>> in short order to what you want, is set YES, so if the warning worked as you
>> hope, it should have triggered.
>>
>> You might have the +load method of the class introspect to see if it
>> implements +initialize, and throw an exception, but that requires a class
>> hierarchy that defeats the purpose of a protocol.
>>
>> — F
>>
>>
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