...
Since
...
a
...
target
...
class
...
is
...
not
...
necessarily
...
designed
...
to
...
be
...
extended
...
by
...
a
...
mixin
...
class,
...
a
...
mixin
...
class
...
might
...
have
...
better
...
ideas
...
on
...
how
...
to
...
implement
...
properties
...
and
...
methods
...
in
...
the
...
target
...
class.
...
In
...
our
...
example,
...
the
...
FloorWaxMixin
...
might
...
desire
...
to
...
override
...
the
...
target
...
class'
...
TasteGood
...
method
...
to
...
a
...
more
...
floorwaxy
...
slogan,
...
like
...
"Luster
...
AND
...
flavor
...
– here
...
comes
...
the
...
dessert
...
wax!".
...
You
...
achieve
...
this
...
by
...
attributing
...
the
...
mixin's
...
implementation
...
of
...
the
...
member
...
to
...
override
...
with
...
OverrideTarget
...
.
...
This
...
requires
...
that
...
the
...
method
...
to
...
override
...
is
...
virtual – just as in plain old inheritance.
| Code Block |
|---|
public class DessertTopping
{
public virtual void TasteGood ()
{
Console.WriteLine ("Mmmmmm, tastes terrific!");
}
}
[Extends (typeof (DessertTopping))]
public class FloorWaxMixin : IFloorWaxMixin
{
public void SealFloor ()
{
Console.WriteLine ("Luster AND flavor -- here comes the dessert wax!");
}
[OverrideTarget]
public void TasteGood ()
{
Console.WriteLine ("Mmmmmm... the yummiest floor-wax ever!");
}
}
{code}
|
Most
...
re-motion
...
mixin
...
will
...
work
...
regardless
...
of
...
who
...
extends
...
whom,
...
and
...
this
...
code
...
is
...
no
...
exception.
...
You
...
can
...
use
...
the
...
OverrideTarget
...
attribute
...
if
...
you
...
extend
...
with
...
the
...
Uses
...
attribute
...
instead
...
of
...
the
...
Extends
...
attribute:
...
| Code Block |
|---|
[Uses (typeof (FloorWaxMixin))]
public class DessertTopping
{
// must be 'virtual' now, so that the mixin can override it
public virtual void TasteGood ()
{
Console.WriteLine ("Mmmmmm, tastes terrific!");
}
}
public class FloorWaxMixin : IFloorWaxMixin
{
public void SealFloor ()
{
Console.WriteLine ("Dirt, grime, even black heel marks -- wipe clean with a damp mop!");
}
[OverrideTarget]
public void TasteGood ()
{
Console.WriteLine ("Mmmmmm... the yummiest floor-wax ever!");
}
}
{code}
h5. Target overrides Mixin?
In |
Target overrides Mixin?
In re-motion
...
mixins,
...
not
...
only
...
can
...
mixin
...
classes
...
override
...
members
...
in
...
the
...
target
...
class,
...
it
...
also
...
works
...
the
...
other
...
way
...
around.
...
This
...
is
...
easy
...
to
...
demonstrate
...
in
...
a
...
toy
...
example
...
and
...
will
...
pose
...
no
...
surprises.
...
Let's
...
say,
...
we
...
want
...
that
...
DessertTopping
...
overrides
...
FloorWax
...
's
...
SealFloor
...
.
...
The
...
following
...
code
...
will
...
NOT
...
work,
...
because
...
the
...
OverrideMixin
...
attribute
...
requires
...
that
...
the
...
mixin
...
class
...
is
...
derived
...
from
...
the
...
generic
...
type
...
Mixin<TThis>
...
,
...
and
...
we
...
have
...
not
...
covered
...
that
...
yet
...
in
...
this
...
tutorial.
...
| Code Block |
|---|
// *** bad sample code ***
// *** won't work ***
[Uses (typeof (FloorWaxMixin))]
public class DessertTopping
{
public virtual void TasteGood ()
{
Console.WriteLine ("Mmmmmm, tastes terrific!");
}
[OverrideMixin]
public virtual void SealFloor ()
{
Console.WriteLine ("You can also seal the floor with it!");
}
}
public class FloorWaxMixin : IFloorWaxMixin
{
public virtual void SealFloor ()
{
Console.WriteLine ("Dirt, grime, even black heel marks -- wipe clean with a damp mop!");
}
}
{code}
|
Apart
...
from
...
the
...
fact
...
that
...
the
...
listing
...
above
...
won't
...
work,
...
alert
...
readers
...
might
...
observe
...
that
...
this
...
example
...
makes
...
very
...
little
...
sense
...
– even
...
in
...
the
...
make-believe
...
world
...
of
...
contrived
...
toy
...
examples
...
this
...
is
...
a
...
bit
...
of
...
a
...
stretch.
...
If
...
DessertTopping
...
has
...
a
...
SealFloor
...
method,
...
isn't
...
it
...
a
...
dessert
...
wax
...
already?
...
Why
...
use
...
a
...
mixin
...
in
...
first
...
place?
...
We
...
will
...
return
...
to
...
the
...
question
...
of
...
overriding
...
mixin
...
methods
...
in
...
section
...
...
...
...
...
...
...
...
,
...
after
...
introducing
...
the
...
generic
...
Mixin<TThis>
...
and
...
Mixin<TThis,
...
TBase>
...
types.
...
Sample
...
code
...
The
...
sample
...
code
...
for
...
this
...
section
...
is
...
stored
...
...
...