1. nested-name-specifier
Kei Hasegawa

2. Look up symbol table while syntax analysis at C language
For regular expression [_a-zA-Z][_a-zA-Z0-9]* (i.e. name) string
Should look up symbol table or not?
Roughly say,
if the type is required at the point, it’s necessary to look up symbol table for searching `typedef-name’
C Compiler (PDF Document)
2.2.1 Lexical analyzer and symbol table

3. And more `::’ at C++ namespace N { } N::outer::inner noi;
struct outer {
// ...
struct inner {
static int si; };
struct S { /* ... */ };
extern double S; // ok : Variable name space separates from tag name space }
N::outer::inner noi;
int N::outer::inner::si;
int N; // error: multiple definition of `N’
double N::S;
struct N::S ns;

4. Part of C++ grammar nested-name-specifier: class-or-namespace-name:
class-or-namespace-name :: nested-name-specifier
class-or-namespace-name ::
...
class-or-namespace-name:
class-name
namespace-name
type-name:

5. Name -> Token
For name X , judge previous token is `::’ and next token is `::’
If previous token is `::’, look up symbol table for X
If not exists, it’s immediately error.
If next token is `::’, look up symbol table for X
If next token is again name (call Y ) , Not looking up symbol table for Y , and determine the token of Y later.
Apply other “Name -> Token rule” for X
Suitably look up symbol table.

6. N::outer::inner noi;
Next token of `N’ is `::’, so look up symbol table for `N’
`N’ is recognized as namespace-name
Previous token of `outer’ is `::’, so look up symbol table for `outer’
`outer’ is recognized as class-name
`outer ::’ are reduced as nested-name-specifier
Previous token of `inner’ is `::’, so look up symbol table for `inner’
`inner’ is recognized as class-name
`inner’ is reduced as type-name unlike `outer’
Previous token of `noi’ is not `::’, and next token of `noi’ is not `::’ either. So the other rule is applied:
In this case, there already exists type at stack of decl_spec, so not look up symbol table

7. Move to scope When class-or-namespace-name is reduced, move to scope:
/* yacc/bison */
class_or_namespace_name
: class_name { scope::current = $1; }
| namespace_name { scope::current = $1; }

8. Move to scope (Continue)
Bellow code doesn’t work:
nested-name-specifier:
class-or-namespace-name :: { scope::current = ...; }
class-or-namespace-name :: { scope::current = ...; } nested-name-specifier
...
Later than previous sheet:
cannot look up `outer’ nor `inner’
Moving to scope before `::’ is correct:
i.e. same as previous sheet.

9. shift/reduce conflict handling
Report file of yacc/bison
State X1
R11 nested_name_specifier: class_or_namespace_name COLONCOLON . nested_name_specifier
R | class_or_namespace_name COLONCOLON .
...
It’s not correct that parser always shifts every class-name token at State X1
Insert bellow code into suitable position of `yyparse’ :
if (yystate == X1 && peek() != COLONCOLON) {
yyn = R12 + 1;
goto yyreduce; }

10. reduce/reduce conflict handling
Report file of yacc/bison
State X2
R21 type_name: class_name .
R22 class_or_namespace_name: class_name .
The rule R22 is not used at this rate.
Insert bellow code into suitable position of `yyparse’ :
if (yystate == X2 && peek() == COLONCOLON) {
yyn = R22 + 1;
goto yyreduce; }

11. Postprocessing for `::’ moving scope
Required restoring the original scope
N::outer::inner
noi;
At this point, scope is root.
At this point, move to root from `N::outer’

12. At this point, scope is parameter scope of N::T::f
At this point, move to parameter scope of N::T::f
At this point, scope is root
void N::T::f
( N2::T2* p) {
N3::T3::x を参照;
At this point, move to body of N::T::f
At this point, scope is body of N::T::f }
At this point, move to root