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Scala Type Parameters & Variance

Type Parameters Similar to C++ templates or Java generics. These can apply to classes, traits or functions. class MyClass[T](arg1: T) { ... } new MyClass[Int](1) new MyClass(1) // the type is being inferred, i.e. determined based on the value arguments It is possible to restrict the type being used, e.g. def myFct[T <: TopLevel](arg: T): T = { ... } // T must derive from TopLevel or be TopLevel def myFct[T >: Level1](arg: T): T = { ... } // T must be a supertype of Level1 def myFct[T >: Level1 <: TopLevel](arg: T): T = { ... } Variance Given A <: B If C[A] <: C[B], C is covariant If C[A] >: C[B], C is contravariant Otherwise C is nonvariant class C[+A] { ... } // C is covariant class C[-A] { ... } // C is contravariant class C[A] { ... } // C is nonvariant For a function, if A2 <: A1 and B1 <: B2, then A1 => B1 <: A2 => B2. Functions must be contravariant in their argument types and covariant in their result types, e.g. t...
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AVR Tutorial - Input / Output

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Overview You cannot imagine to use microcontroller without using any of its i/o pins. Finally its all about : taking input , processing it and generating output ! Thus i/o registers and their correct settings is indispensable part while learning to program any uC. We will learn how to use AVR ports and actually ‘code’ for writing/reading data to/from port pins. It is slightly confusing for beginners, however once you understand it, you will certainly appreciate the way it is designed. NOTE : I will frequently refer to ‘configuring pin’ or simply ‘pin’. Remember, a port has multiple pins. Thus in order to change setting for one port, you have to change setting for all port pins of that port. To change setting for one single pin of the port, you have to change a particular bit in associated register. Got that ? If not read this para again. Registers AVR is 8 bit microcontroller. All its ports are 8 bit wide. Every port has 3 registers associated with it each one with 8 bits...
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EJB - Intro to Session beans

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What is a Session bean A session bean is the enterprise bean that directly interact with the user and contains the business logic of the enterprise application . A session bean represents a single client accessing the enterprise application deployed on the server by invoking its method. An application may contain multiple sessions depending upon the number of users accessing to the application. A session bean makes an interactive session only for a single client and shields that client from complexities just by executing the business task on server side. For example, whenever a client wants to perform any of these actions such as making a reservation or validating a credit card, a session bean should be used. The session bean decides what data is to be modified. Typically, the session bean uses an entity bean to access or modify data. They implement business logic, business rules, algorithms, and work flows. Session beans are relatively short-lived components. The EJB container may...
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