<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
the	O
single-serving	B-Language
visitor	I-Language
pattern	I-Language
is	O
a	O
design	O
pattern	O
.	O
</s>
<s>
Its	O
intent	O
is	O
to	O
optimise	O
the	O
implementation	O
of	O
a	O
visitor	B-Language
that	O
is	O
allocated	O
,	O
used	O
only	O
once	O
,	O
and	O
then	O
deleted	O
(	O
which	O
is	O
the	O
case	O
of	O
most	O
visitors	O
)	O
.	O
</s>
<s>
The	O
single-serving	B-Language
visitor	I-Language
pattern	I-Language
should	O
be	O
used	O
when	O
visitors	O
do	O
not	O
need	O
to	O
remain	O
in	O
memory	O
.	O
</s>
<s>
This	O
is	O
often	O
the	O
case	O
when	O
visiting	O
a	O
hierarchy	O
of	O
objects	O
(	O
such	O
as	O
when	O
the	O
visitor	B-Language
pattern	I-Language
is	O
used	O
together	O
with	O
the	O
composite	O
pattern	O
)	O
to	O
perform	O
a	O
single	O
task	O
on	O
it	O
,	O
for	O
example	O
counting	O
the	O
number	O
of	O
cameras	O
in	O
a	O
3D	O
scene	O
.	O
</s>
<s>
The	O
regular	O
visitor	B-Language
pattern	I-Language
should	O
be	O
used	O
when	O
the	O
visitor	B-Language
must	O
remain	O
in	O
memory	O
.	O
</s>
<s>
This	O
occurs	O
when	O
the	O
visitor	B-Language
is	O
configured	O
with	O
a	O
number	O
of	O
parameters	O
that	O
must	O
be	O
kept	O
in	O
memory	O
for	O
a	O
later	O
use	O
of	O
the	O
visitor	B-Language
(	O
for	O
example	O
,	O
for	O
storing	O
the	O
rendering	O
options	O
of	O
a	O
3D	O
scene	O
renderer	O
)	O
.	O
</s>
<s>
However	O
,	O
if	O
there	O
should	O
be	O
only	O
one	O
instance	O
of	O
such	O
a	O
visitor	B-Language
in	O
a	O
whole	O
program	O
,	O
it	O
can	O
be	O
a	O
good	O
idea	O
to	O
implement	O
it	O
both	O
as	O
a	O
single-serving	O
visitor	B-Language
and	O
as	O
a	O
singleton	O
.	O
</s>
<s>
In	O
doing	O
so	O
,	O
it	O
is	O
ensured	O
that	O
the	O
single-serving	O
visitor	B-Language
can	O
be	O
called	O
later	O
with	O
its	O
parameters	O
unchanged	O
(	O
in	O
this	O
particular	O
case	O
"	O
single-serving	O
visitor	B-Language
"	O
is	O
an	O
abuse	O
of	O
language	O
since	O
the	O
visitor	B-Language
can	O
be	O
used	O
several	O
times	O
)	O
.	O
</s>
<s>
The	O
single-serving	O
visitor	B-Language
is	O
called	O
through	O
the	O
intermediate	O
of	O
static	O
methods	O
.	O
</s>
<s>
With	O
a	O
single-serving	O
visitor	B-Language
,	O
it	O
is	O
ensured	O
that	O
visitors	O
are	O
allocated	O
when	O
needed	O
and	O
destroyed	O
once	O
useless	O
.	O
</s>
<s>
A	O
simpler	O
interface	O
than	O
visitor	B-Language
.	O
</s>
<s>
The	O
visitor	B-Language
is	O
created	O
,	O
used	O
and	O
free	O
by	O
the	O
sole	O
call	O
of	O
the	O
apply_to	O
static	O
method	O
.	O
</s>
<s>
At	O
each	O
call	O
of	O
the	O
apply_to	O
method	O
,	O
a	O
single-serving	O
visitor	B-Language
is	O
created	O
then	O
discarded	O
,	O
which	O
is	O
time-consuming	O
.	O
</s>
<s>
If	O
the	O
single-serving	O
visitor	B-Language
has	O
to	O
be	O
initialised	O
,	O
the	O
parameters	O
have	O
to	O
be	O
passed	O
through	O
the	O
static	O
method	O
:	O
</s>
