<s>
In	O
software	B-General_Concept
engineering	I-General_Concept
,	O
a	O
unity	B-Language
build	I-Language
(	O
also	O
known	O
as	O
unified	B-Language
build	I-Language
or	O
jumbo	B-Language
build	I-Language
)	O
is	O
a	O
method	O
used	O
in	O
C	B-Language
and	O
C++	B-Language
software	O
development	O
to	O
speed	O
up	O
the	O
compilation	O
of	O
projects	O
by	O
combining	O
multiple	O
translation	B-Language
units	I-Language
into	O
a	O
single	O
one	O
,	O
usually	O
achieved	O
by	O
using	O
include	B-Language
directives	I-Language
to	O
bundle	O
multiple	O
source	O
files	O
into	O
one	O
larger	O
file	O
.	O
</s>
<s>
then	O
header.h	O
will	O
be	O
processed	O
only	O
once	O
(	O
thanks	O
to	O
include	B-Language
guards	I-Language
)	O
when	O
compiling	O
jumbo_file.cc	O
.	O
</s>
<s>
The	O
main	O
benefit	O
of	O
unity	B-Language
builds	I-Language
is	O
a	O
reduction	O
of	O
duplicated	O
effort	O
in	O
parsing	O
and	O
compiling	O
the	O
content	O
of	O
headers	O
that	O
are	O
included	O
in	O
more	O
than	O
one	O
source	O
file	O
.	O
</s>
<s>
The	O
content	O
of	O
headers	O
usually	O
accounts	O
for	O
the	O
majority	O
of	O
code	O
in	O
a	O
source	O
file	O
after	O
preprocessing	B-Language
.	O
</s>
<s>
Unity	B-Language
builds	I-Language
also	O
mitigate	O
the	O
overhead	O
due	O
to	O
having	O
a	O
large	O
number	O
of	O
small	O
source	O
files	O
by	O
reducing	O
the	O
number	O
of	O
object	O
files	O
created	O
and	O
processed	O
by	O
the	O
compilation	O
chain	O
,	O
and	O
allows	O
interprocedural	O
analysis	O
and	O
optimisation	O
across	O
the	O
files	O
that	O
form	O
the	O
unity	B-Language
build	I-Language
task	O
(	O
similar	O
to	O
the	O
effects	O
of	O
link-time	O
optimisation	O
)	O
.	O
</s>
<s>
They	O
make	O
it	O
also	O
easier	O
to	O
detect	O
violations	O
of	O
the	O
One	B-Language
Definition	I-Language
Rule	I-Language
,	O
because	O
if	O
a	O
symbol	O
is	O
defined	O
twice	O
in	O
different	O
source	O
files	O
in	O
the	O
same	O
unity	B-Language
build	I-Language
,	O
the	O
compiler	O
will	O
be	O
able	O
to	O
identify	O
the	O
redefinition	O
and	O
emit	O
a	O
warning	O
or	O
error	O
.	O
</s>
<s>
One	O
of	O
the	O
drawbacks	O
of	O
unity	B-Language
builds	I-Language
is	O
a	O
larger	O
memory	O
footprint	O
due	O
to	O
larger	O
translation	B-Language
units	I-Language
.	O
</s>
<s>
Larger	O
translation	B-Language
units	I-Language
can	O
also	O
negatively	O
affect	O
parallel	O
builds	O
,	O
since	O
a	O
small	O
number	O
of	O
large	O
compile	O
jobs	O
is	O
generally	O
harder	O
or	O
impossible	O
to	O
schedule	O
to	O
saturate	O
all	O
available	O
parallel	O
computing	O
resources	O
effectively	O
.	O
</s>
<s>
Unity	B-Language
builds	I-Language
can	O
also	O
deny	O
part	O
of	O
the	O
benefits	O
of	O
incremental	O
builds	O
,	O
that	O
rely	O
on	O
rebuilding	O
as	O
little	O
code	O
as	O
possible	O
,	O
i.e.	O
</s>
<s>
only	O
the	O
translation	B-Language
units	I-Language
affected	O
by	O
changes	O
since	O
the	O
last	O
build	O
.	O
</s>
<s>
Unity	B-Language
builds	I-Language
have	O
also	O
potentially	O
dangerous	O
effects	O
on	O
the	O
semantics	B-Application
of	O
programs	O
.	O
</s>
<s>
Some	O
valid	O
C++	B-Language
constructs	O
that	O
rely	O
on	O
internal	O
linkage	O
may	O
fail	O
under	O
a	O
unity	B-Language
build	I-Language
,	O
for	O
instance	O
clashes	O
of	O
static	O
symbols	O
and	O
symbols	O
defined	O
in	O
anonymous	O
namespaces	O
with	O
the	O
same	O
identifier	O
in	O
different	O
files	O
.	O
</s>
<s>
If	O
different	O
C++	B-Language
files	O
define	O
different	O
functions	O
with	O
the	O
same	O
name	O
,	O
the	O
compiler	O
may	O
unexpectedly	O
resolve	O
the	O
overloading	B-Language
by	O
selecting	O
the	O
wrong	O
function	O
,	O
in	O
a	O
way	O
that	O
was	O
not	O
possible	O
when	O
designing	O
the	O
software	O
with	O
the	O
files	O
as	O
different	O
translation	B-Language
units	I-Language
.	O
</s>
<s>
Some	O
build	O
systems	O
provide	O
built-in	O
support	O
for	O
automated	O
unity	B-Language
builds	I-Language
,	O
including	O
Visual	B-Application
Studio	I-Application
,	O
Meson	B-Application
and	O
CMake	B-Language
.	O
</s>
