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From: _SmilingVishal
Message 5 in Discussion
Hi, Abstraction is selective ignorance.An abstract type provides a group of related
functions whose joint actions completely define the abstraction as far as its uses are
concerned. The irrelevant details of how the abstraction is supported are completely
hidden. If you are a C programmer, think of a class as an extension of the struct
type. A struct contains predefined data types, for example, char or int, and might
also contain other struct types. C++ allows a struct type to have not only data types
to store data, but also operations to manipulate the data. The C++ keyword class is
analogous to struct in C.
C++ provides classes as a means for data abstraction. You decide what types (classes)
you want for your program data and then decide what operations each type needs. In
other words, a C++ class is a user-defined data type.
For example, if you define a class BigNum, which implements arithmetic for very large
integers, you can define the + operator so that it has a meaning when used with
objects in the class BigNum. e.g if n1 and n2 are objects of the type BigNum, then the
expression n1 + n2 has a value determined by your definition of + for BigNum.
An abstract data type is an existential type.
The important thing about an abstract type is that there exists a data type that
solves some requirement equations.If, in addition, the set of the data type
solutions obeys some (syntactic) structural rules, then parametric poly-morphism
may be used to provide a uniform implementation.
For Example:
template<class T, class Container = deque<T> >
class stack {
protected:Container c;
public:
bool empty() const { return c.empty(); }
value_type& top(){ return c.back(); }
const value_type& top() const{ return c.back(); }
void push(const value_type& x){ c.push_back(x); }
void pop(){ c.pop_back(); }
};
Regards,
_SmilingVishal
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