Objective-C Language Basic Data Types IMP (implementation pointer)
Example
IMP is a C type referring to the implementation of a method, also known as an implementation pointer. It is a pointer to the start of a method implementation.
Syntax:
id (*IMP)(id, SEL, …)
IMP is defined by:
typedef id (*IMP)(id self,SEL _cmd,…);
To access this IMP, the message “methodForSelector” can be used.
Example 1:
IMP ImpDoSomething = [myObject methodForSelector:@selector(doSomething)];
The method adressed by the IMP can be called by dereferencing the IMP.
ImpDoSomething(myObject, @selector(doSomething));
So these calls are equal:
myImpDoSomething(myObject, @selector(doSomething));
[myObject doSomething]
[myObject performSelector:mySelector]
[myObject performSelector:@selector(doSomething)]
[myObject performSelector:NSSelectorFromString(@"doSomething")];
Example :2:
SEL otherWaySelector = NSSelectorFromString(@“methodWithFirst:andSecond:andThird:");
IMP methodImplementation = [self methodForSelector:otherWaySelector];
result = methodImplementation( self,
betterWaySelector,
first,
second,
third );
NSLog(@"methodForSelector : %@", result);
Here, we call [NSObject methodForSelector which returns us a pointer to the C function that actually implements the method, which we can the subsequently call directly.
