Creating Structs
You create
an instance of a struct by using the new
keyword
in an assignment statement, just as you would for a class. In Example 7-1, the
Tester
class creates an instance of
Location
as follows:
Location loc1 = new Location(200,300);
Here the new instance is named loc1
and is passed
two values, 200
and 300
.
Structs as Value Types
The definition of the Tester
class in Example 7-1 includes a
Location
object, loc1
, created
with the values 200
and 300
.
This line of code calls the Location
constructor:
Location loc1 = new Location(200,300);
Then WriteLine( )
is called:
Console.WriteLine("Loc1 location: {0}", loc1);
WriteLine( )
is expecting an object; but, of
course, Location
is a struct (a value type). The
compiler automatically boxes the struct (as it would any value type),
and it is the boxed object that is passed to WriteLine( )
. ToString( )
is called on the boxed object, and because the struct (implicitly)
inherits from object
, it is able to respond
polymorphically, overriding the method just as any other object
might:
Loc1 location: 200, 300
Structs are value objects, however, and when passed to a function,
they are passed by value, as seen in the next line of code, in which
the loc1
object is passed to the myFunc( )
method:
t.myFunc(loc1);
In myFunc
new values are assigned to
x
and y
, and then these new
values are printed out:
Loc1 location: 50, 100
When you return to the calling function (Main( )
) and call WriteLine( )
again, the values are unchanged:
Loc1 location: ...
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