What is the difference between Forward Declaration and import ??

I may be wrong but if I remember right, I believe forward declarations are mainly to avoid circular imports, where one file imports another file which imports the first file etc.... Basically when you import a file, the contents of that file are substituted at the point of import when you build your project, which is then fed to the compiler. If you have circular imports, you'd have an infinite loop which would never compile. Fortunately xcode will tell you about this before trying. The forward declaration says "Don't import this class but just know that it exists. " Without either an import or a forward declaration, you get an error that no such class exists.