notesscopes.txt

C Preprocessor,antlr的grammar语言描述,用于学习词法分析,语法分析

Notes re scopes 

The current system of maintaining and using scope information is relatively
	simplistic but appears to be reasonably effective. However, it has caused
	some productions to be more complex than would otherwise be the case.

The current scope level is held in Dictionary.hpp as "int currentScope".

	"currentScope" is initialised to zero by constructor for dictionary.cpp 
		when "class symbols" is constructed in CPPParser.init() in 
		CPPParser.cpp (generated from CPP_parser.g)

	CPPParser.init() then sets "templateParameterScope" to zero with
		templateParameterScope = symbols->getCurrentScopeIndex();

		This top level scope is not currently being used but is kept in reserve
		in case of some future need.

	CPPParser.init() then sets "externalScope" to 1 with,
		symbols->saveScope();	// Advance currentScope from 0 to 1
		externalScope = symbols->getCurrentScopeIndex();

		"externalScope" is used for all type names and template parameter names
		and they remain in place from declaration to the end of the parse.

	CPPParser.init() then declares "std" in external scope and the scope level
		advanced to 2 for local scopes
		CPPSymbol *a = new CPPSymbol("std", CPPSymbol::otTypedef);
		symbols->define("std", a);
		symbols->saveScope();	// Advance currentScope from 1 to 2 (and higher)
		for all other symbols which are treated as locals

The value "currentScope" is obtained using "dictionary->getCurrentScopeIndex()"

Local scopes increase "currentScope" by 1 for each nested local scope.

Variables declared after types with identical names used to hide the typename but
	now a search for an identical typename will find it.

At the end of each local scope "currentScope" is reduced by 1 and all variables
	(not typenames) declared in the scope are removed from the dictionary.

At the end of a parse "exitExternalScope() in Support.cpp is entered via 
	"translation_unit" in CPP_parser.g which then reduces the remaining scope 
	level by 1 twice. If this reduces "current Scope" to 0 a good end message is
	displayed, otherwise a warning message is displayed.

Version 3.1 November 2005