symbol.hpp File Reference

Marker types to indicate a literal string and a Symbol. More...

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Description

Marker types to indicate a literal string and a Symbol.

Instead of working just with pointers, which could represent pretty much anything, it is prudent to express the meaning at interfaces and for variables and members explicitly.

On conceptual level, while a string is just some sequence of characters and nothing can be said about its mutability or lifetime, a Literal is explicitly meant to be static. It is a fixed sequence of characters placed in a stable memory location and assumed to exist during the whole lifetime of the execution. The concept of a Symbol is slightly different: it is meant to be a distinguishable, fixed, unique token. An Identical sequence of characters means we have exactly the same Symbol.

These concepts can be fused by treating Symbol as a specialisation of Literal, additionally maintaining an automatically populated, static symbol table, and we close the circle by allowing Symbol instances to be created from strings at runtime.

Remarks

this abstraction was first used occasionally 11/2008, at that time just as a typedef to mark assumption on the new interfaces for rules based configuration in the Steam-Layer. Over time, conversions, comparison and hashcode implementation were added. It turned out that the most smooth integration in coding practice is achieved when allowing transparent conversion between Literal ⟷ CStr, but not for Symbol or std::string.

Todo:

9/2017 consider this mostly as settled, but might require some finishing touches

• maybe improve interoperation of Symbol and std::string
• investigate performance of the automatic symbol table
• improve Lifecycle in startup and shutdown phase
• maybe some metaprogramming magic to build distinct types based on symbols.

See also

symbol-impl.cpp

configrules.hpp

query.hpp

Definition in file symbol.hpp.

#include "lib/hash-standard.hpp"
#include <string>
#include <cstring>

Namespaces
namespace	lib
	Implementation namespace for support and library code.
namespace	lib::anonymous_namespace{symbol.hpp}

Typedefs
using	CStr = const char *

Classes
class	Literal
	Inline string literal. More...
class	Symbol
	Token or Atom with distinct identity. More...

Functions
CStr	cStr (std::string const &rendered)
	convenience shortcut: forced conversion to c-String via string.
constexpr int	strNcmp (CStr a, CStr b, size_t len)
HashVal	hash_value (Literal literal)
	generate hash value based on the Literal's contents.
HashVal	hash_value (Symbol sym)
	hash value for Symbols is directly based on the symbol table entry
constexpr bool	operator== (Literal const &s1, Literal const &s2)
constexpr bool	operator== (Symbol const &s1, Symbol const &s2)
constexpr bool	operator== (CStr s1, Literal s2)
constexpr bool	operator== (Symbol s1, CStr s2)
constexpr bool	operator== (Literal s1, Symbol s2)
constexpr bool	operator== (Literal s1, std::string const &s2)
constexpr bool	operator== (Symbol s1, std::string const &s2)
std::string	operator+ (std::string str, Literal const &sym)
	string concatenation
std::string	operator+ (Literal const &sym, std::string str)

Typedef Documentation

CStr

using CStr = const char*

Definition at line 55 of file symbol.hpp.

Function Documentation

cStr()

CStr cStr ( std::string const &  rendered )

inline

convenience shortcut: forced conversion to c-String via string.

usable for printf with objects providing to-string conversion.

Definition at line 60 of file symbol.hpp.

Referenced by Asset::Asset(), CompletedDefinition< SIG >::CompletedDefinition(), Config::Config(), TestSource::TestSource(), AppState::abort(), Command::activate(), UiStyle::addStockIconFromPath(), DiffLanguage< I, E >::DiffStep::applyTo(), Proxy< IHandle >::cycle(), Proxy< IHandle >::displayInfo(), TreeDiffMutatorBinding::emu(), HandlingPattern::invoke(), test::anonymous_namespace{suite.cpp}::invokeTestCase(), lumiera_get_plugin_path_default(), lumiera::error::lumiera_unexpectedException(), Proxy< IHandle >::markError(), Proxy< IHandle >::markNote(), AppState::maybeStart(), TreeDiffMutatorBinding::mut(), SessionCommandFunction_test::perform_massivelyParallel(), DispatcherLoop::processCommands(), steam::asset::meta::anonymous_namespace{time-grid.cpp}::publishWrapped(), lib::resolveModulePath(), SessionElementQuery_test::run(), MockSys::run(), UiStyle::setTheme(), PrintfFormatter< NUM, len >::show(), SubsystemRunner::sigTerm(), util::sNum(), MockSys::start(), Proxy< IHandle >::triggerGuiShutdown(), NotificationService::triggerGuiShutdown(), MockSys::triggerShutdown(), SubsystemRunner::triggerStartup(), and util::uNum().

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