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Why is the Objective-C object type called 'id'? As opposed to, say, 'object'?
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id is the generic object pointer, an Objective-C type representing "any object". An instance of any Objective-C class can be stored in an id variable.
In C language, an identifier is a combination of alphanumeric characters, i.e. first begin with a letter of the alphabet or an underline, and the remaining are letter of an alphabet, any numeric digit, or the underline.
In Swift 3, the id type in Objective-C now maps to the Any type in Swift, which describes a value of any type, whether a class, enum, struct, or any other Swift type.
Dynamic typing allows us to declare a variable that is capable of storing any type of object, regardless of its class origins. This is achieved using the Objective-C id type. The idtype is a special, general purpose data type that can be assigned an object of any type.
It is called id because that, literally, is all the type represents - an identifier.
Quoting Brad Cox from Object Oriented Programming: an Evolutionary Approach (actually, the first edition, one of the first OO books I bought): An id consumes a fixed amount of space, wide enough to identify as many objects as may exist at any one time. This space is not the same as the space occupied by the private data in the object itself. Object identifiers are fixed-sized numbers,...
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