A Selector in Objective-C can be seen as an equivalent to a procedural type in Object Pascal.
In difference with the procedural type, Objective-C has only one selector type: SEL. It is defined in the objc unit – which is automatically included in the uses clause of any unit compiled with the objectivec1 modeswitch.
To assign a value to a variable of type SEL, the objcselector method must be used:
The objc unit contains methods to manipulate and use the selector.