<s>
The	O
most	B-Language
vexing	I-Language
parse	I-Language
is	O
a	O
counterintuitive	O
form	O
of	O
syntactic	O
ambiguity	O
resolution	O
in	O
the	O
C++	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
In	O
certain	O
situations	O
,	O
the	O
C++	B-Language
grammar	O
cannot	O
distinguish	O
between	O
the	O
creation	O
of	O
an	O
object	O
parameter	O
and	O
specification	O
of	O
a	O
function	O
's	O
type	O
.	O
</s>
<s>
The	O
term	O
"	O
most	B-Language
vexing	I-Language
parse	I-Language
"	O
was	O
first	O
used	O
by	O
Scott	O
Meyers	O
in	O
his	O
2001	O
book	O
Effective	O
STL	O
.	O
</s>
<s>
While	O
unusual	O
in	O
C	B-Language
,	O
the	O
phenomenon	O
was	O
quite	O
common	O
in	O
C++	B-Language
until	O
the	O
introduction	O
of	O
uniform	O
initialization	O
in	O
C++11	B-Language
.	I-Language
</s>
<s>
However	O
,	O
C	B-Language
allows	O
superfluous	O
parentheses	O
around	O
function	O
parameter	O
declarations	O
;	O
in	O
this	O
case	O
,	O
the	O
declaration	O
of	O
i	O
is	O
instead	O
a	O
function	O
declaration	O
equivalent	O
to	O
the	O
following	O
:	O
</s>
<s>
The	O
C++	B-Language
standard	O
requires	O
the	O
second	O
interpretation	O
,	O
which	O
is	O
inconsistent	O
with	O
line	O
9	O
above	O
.	O
</s>
<s>
For	O
example	O
,	O
Clang++	B-Application
warns	O
that	O
the	O
most	B-Language
vexing	I-Language
parse	I-Language
has	O
been	O
applied	O
on	O
line	O
9	O
and	O
errors	O
on	O
the	O
following	O
line	O
:	O
</s>
<s>
Function	O
types	O
in	O
C++	B-Language
are	O
usually	O
hidden	O
behind	O
typedefs	B-Language
and	O
typically	O
have	O
an	O
explicit	O
reference	B-Language
or	O
pointer	O
qualifier	O
.	O
</s>
<s>
In	O
the	O
variable	O
declaration	O
example	O
,	O
the	O
preferred	O
method	O
(	O
since	O
C++11	B-Language
)	O
is	O
uniform	O
(	O
brace	O
)	O
initialization	O
.	O
</s>
<s>
This	O
also	O
allows	O
limited	O
omission	O
of	O
the	O
type	O
name	O
entirely:Prior	O
to	O
C++11	B-Language
,	O
the	O
common	O
techniques	O
to	O
force	O
the	O
intended	O
interpretation	O
were	O
use	O
of	O
an	O
extra	O
parenthesis	O
or	O
copy-initialization:In	O
the	O
latter	O
syntax	O
,	O
the	O
copy-initialization	O
is	O
likely	O
to	O
be	O
optimized	B-Application
out	I-Application
by	O
the	O
compiler	O
.	O
</s>
<s>
Since	O
C++17	B-Language
,	O
this	O
optimization	O
is	O
guaranteed	O
.	O
</s>
