symbols.md

Symbols (SYMSXP)

Rboolean Rf_isSymbol(SEXP s);

Create

If symbol exists, return it; otherwise create it. SYMSXPs don’t need to be protected because symbols are not currently reclaimed by the garbage collector. If you are using a symbol many times, it may be worth caching it to avoid repeated lookups.

SEXP Rf_install(const char *);
SEXP Rf_installChar(SEXP);

Mising symbol

R_MissingArg represents the missing/empty symbol, i.e. the second argument in this call f(x, ).

Predefined symbols

A number of symbols are so commonly used, they’re predefined and exported:

  • R_dot_defined: “.defined”
  • R_dot_Method: “.Method”
  • R_dot_packageName: “.packageName”
  • R_dot_target: “.target”
  • R_BaseSymbol: “base”
  • R_BraceSymbol: “{”
  • R_Bracket2Symbol: “[[”
  • R_BracketSymbol: “[”
  • R_ClassSymbol: “class”
  • R_DeviceSymbol: “.Device”
  • R_DimNamesSymbol: “dimnames”
  • R_DimSymbol: “dim”
  • R_DollarSymbol: “$”
  • R_DotsSymbol: “…”
  • R_DoubleColonSymbol: “::”
  • R_DropSymbol: “drop”
  • R_LastvalueSymbol: “.Last.value”
  • R_LevelsSymbol: “levels”
  • R_ModeSymbol: “mode”
  • R_NaRmSymbol: “na.rm”
  • R_NameSymbol: “name”
  • R_NamesSymbol: “names”
  • R_NamespaceEnvSymbol: “.__NAMESPACE__.”
  • R_PackageSymbol: “package”
  • R_PreviousSymbol: “previous”
  • R_QuoteSymbol: “quote”
  • R_RowNamesSymbol: “row.names”
  • R_SeedsSymbol: “.Random.seed”
  • R_SortListSymbol: “sort.list”
  • R_SourceSymbol: “source”
  • R_SpecSymbol: “spec”
  • R_TripleColonSymbol: “:::”
  • R_TspSymbol: “tsp”

Internals

// The value of the symbol, as a CHARSXP
// Use CHAR(PRINTNAME(x)) to get the name as a const char*
SEXP (PRINTNAME)(SEXP x);
void SET_PRINTNAME(SEXP x, SEXP v);

SEXP (SYMVALUE)(SEXP x);
void SET_SYMVALUE(SEXP x, SEXP v);

SEXP (INTERNAL)(SEXP x);
void SET_INTERNAL(SEXP x, SEXP v);

int  (DDVAL)(SEXP x);
void (SET_DDVAL)(SEXP x, int v);
SEXP Rf_installDDVAL(int i);