C++ for Scientists - Technische Universität Dresden

76 CHAPTER 3. CLASSES
}
return ∗this;
In fact every class implementation where the copy assignment and the copy constructor have
essential differences in their implementation are very confusing in their behavior and should not
be used, cf. [SA05, p. 94]. The two operations differ in the respect that a constructor creates
content in a new object while an assignment replaces content in an existing object. However,
both the creation as well as the replacement is performed with a copy semantics and the two
operations should behave consistently therefore.
An assignment of an object to itself (source and target have the same address) can be skipped,
line 3 and 4. In line 5 it is tested whether the assignment is a legal operation by checking
the equality of their size. Alternatively the assignment could resize the target if the sizes are
different but that does not correspond to the authors’ understanding of vector behavior — or
can you think of a context in mathematics or physics where a vector space all of a sudden
changes its dimension.
3.6 Automatically Generated Operators
If you define a class without operators C ++ will generate the following four:
• Default constructor;
• Copy constructor;
• Destructor; and
• Copy assignment.
Assume you have a class without any function but with some member variables like this:
class my class
{
type1 var1;
type2 var2;
// ...
typen varn;
};
Then the compiler adds the four operators and your class behaves as you would have written:
class my class
{
public:
my class()
: var1(),
var2(),
// ...
varn()
{}
my class(const my class& that)
: var1(that.var1),
var2(that.var2),