optional

Use this attribute to make an Objective-C interface method optional.

An optional method is a method that does **not** have to be implemented in the class that implements the interface. To safely call an optional method, a runtime check should be performed to make sure the receiver implements the method.

This is a special compiler recognized attribute, it has several requirements, which all will be enforced by the compiler:

* The attribute can only be attached to methods which have Objective-C linkage. That is, a method inside an interface declared as extern (Objective-C)

* It can only be used for methods that are declared inside an interface * It can only be used once in a method declaration * It cannot be attached to a method that is a template

Examples

import core.attribute : optional, selector;

extern (Objective-C):

struct objc_selector;
alias SEL = objc_selector*;

SEL sel_registerName(in char* str);

extern class NSObject
{
    bool respondsToSelector(SEL sel) @selector("respondsToSelector:");
}

interface Foo
{
    @optional void foo() @selector("foo");
    @optional void bar() @selector("bar");
}

class Bar : NSObject
{
    static Bar alloc() @selector("alloc");
    Bar init() @selector("init");

    void bar() @selector("bar")
    {
    }
}

extern (D) void main()
{
    auto bar = Bar.alloc.init;

    if (bar.respondsToSelector(sel_registerName("bar")))
        bar.bar();
}

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