Question

What is the purpose of using a selector here?

CADisplayLink* displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(render:)];

Source: Code from a beginner OpenGL es 2.0 site

I read the definition

The @selector() directive lets you refer to the compiled selector,
rather than to the full method name.

Unfortunetly, this does not clear it up for me. My expertise is in C#. So I appreciate it if you can relate the answer to how a similar solution might be achieved in C#.

Answer 1

A selector declares the name of a function. That’s it. It’s very similar to the Reflection class MethodInfo, but it’s much simpler to use.

Comparison of C# and Objective-C:
Notice the C# code may be a bit off, as I haven’t worked with it in a long time

// C#
using namespace system.reflection;

class someClass {
     void someMethod(object input) {
           string methodName = "doSomething";

           input.getType().getMethod(methodName).invoke(input, new Object[] { });
     }
}

// OBJC
@implementation someClass 

-(void) someMethod:(id) input
{
     SEL methodName = @selector(doSomething);

     [input performSelector:methodName];
}

@end

As far as the internals of a SEL are concerned, it is a C-string that has been put into a private map for speed in lookup at runtime.