Add DATAPTR_RW for use in ALTREP Dataptr methods.

git-svn-id: https://svn.r-project.org/R/trunk@89022 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: luke

doc/manual/R-exts.texi

@@ -14969,14 +14969,15 @@ iteration strategy.
 Some functions useful in implementing new alternate representation
 classes, beyond those defined in @file{R_ext/Altrep.h}, include
 @code{ALTREP}, @code{ALTREP_CLASS}, @code{R_altrep_data1},
-@code{R_set_altrep_data1}, @code{R_altrep_data2}, and
-@code{R_set_altrep_data2}.
+@code{R_set_altrep_data1}, @code{R_altrep_data2},
+@code{R_set_altrep_data2}, and @code{DATAPTR_RW}.
 @eapifun ALTREP
 @eapifun ALTREP_CLASS
 @eapifun R_altrep_data1
 @eapifun R_set_altrep_data1
 @eapifun R_set_altrep_data2
 @eapifun R_altrep_data2
+@eapifun DATAPTR_RW
 @eapihdr R_ext/Altrep.h
 
 For some objects it may be possible to very efficiently determine
@@ -17497,8 +17498,11 @@ functions that should be used instead:
 @itemx DATAPTR
 @itemx STDVEC_DATAPTR
        Use @code{STRING_PTR_RO} and @code{DATAPTR_RO}. Obtaining
-        writable pointers to these data can violate the memory manager's
-        integrity assumptions and is not supported.
+       writable pointers to these data can violate the memory manager's
+       integrity assumptions and is not supported.
+       One exception is that a writable pointer may need to be returned
+       by an @code{ALTREP} @code{Dataptr} method. The function
+       @code{DATAPTR_RW}  can use for this purpose.
 @item isFrame
       Use @code{Rf_isDataFrame}, added in @R{} 4.5.0.
 @item BODY
@@ -17742,6 +17746,10 @@ void CLEAR_ATTRIB(SEXP x)
     UNSET_S4_OBJECT(x);
 @}
 #endif
+
+#if R_VERSION < R_Version(4, 6, 0)
+# define DATAPTR_RW(x) DATAPTR(x)
+#endif
 @end example
 
 

src/include/R_ext/Altrep.h

@@ -172,6 +172,10 @@ DECLARE_METHOD_SETTER(altstring, No_NA)
 DECLARE_METHOD_SETTER(altlist, Elt)
 DECLARE_METHOD_SETTER(altlist, Set_elt)
 
+/* DATAPTR_RW is declared here since it should only be used to
+   implement Dataptr methods. */
+void *DATAPTR_RW(SEXP);
+
 #ifdef  __cplusplus
 }
 #endif

src/main/altclasses.c

@@ -183,13 +183,13 @@ static void *compact_intseq_Dataptr(SEXP x, Rboolean writeable)
 	SET_COMPACT_SEQ_EXPANDED(x, val);
 	UNPROTECT(1);
     }
-    return DATAPTR(COMPACT_SEQ_EXPANDED(x));
+    return DATAPTR_RW(COMPACT_SEQ_EXPANDED(x));
 }
 
 static const void *compact_intseq_Dataptr_or_null(SEXP x)
 {
     SEXP val = COMPACT_SEQ_EXPANDED(x);
-    return val == R_NilValue ? NULL : DATAPTR(val);
+    return val == R_NilValue ? NULL : DATAPTR_RO(val);
 }
 
 static int compact_intseq_Elt(SEXP x, R_xlen_t i)
@@ -428,13 +428,13 @@ static void *compact_realseq_Dataptr(SEXP x, Rboolean writeable)
 	SET_COMPACT_SEQ_EXPANDED(x, val);
 	UNPROTECT(1);
     }
-    return DATAPTR(COMPACT_SEQ_EXPANDED(x));
+    return DATAPTR_RW(COMPACT_SEQ_EXPANDED(x));
 }
 
 static const void *compact_realseq_Dataptr_or_null(SEXP x)
 {
     SEXP val = COMPACT_SEQ_EXPANDED(x);
-    return val == R_NilValue ? NULL : DATAPTR(val);
+    return val == R_NilValue ? NULL : DATAPTR_RO(val);
 }
 
 static double compact_realseq_Elt(SEXP x, R_xlen_t i)
@@ -759,13 +759,13 @@ static R_INLINE void expand_deferred_string(SEXP x)
 static void *deferred_string_Dataptr(SEXP x, Rboolean writeable)
 {
     expand_deferred_string(x);
-    return DATAPTR(DEFERRED_STRING_EXPANDED(x));
+    return DATAPTR_RW(DEFERRED_STRING_EXPANDED(x));
 }
 
 static const void *deferred_string_Dataptr_or_null(SEXP x)
 {
     SEXP state = DEFERRED_STRING_STATE(x);
-    return state != R_NilValue ? NULL : DATAPTR(DEFERRED_STRING_EXPANDED(x));
+    return state != R_NilValue ? NULL : DATAPTR_RO(DEFERRED_STRING_EXPANDED(x));
 }
 
 static SEXP deferred_string_Elt(SEXP x, R_xlen_t i)
@@ -1528,7 +1528,7 @@ static R_xlen_t wrapper_Length(SEXP x)
 static void *wrapper_Dataptr(SEXP x, Rboolean writeable)
 {
     if (writeable)
-	return DATAPTR(WRAPPER_WRAPPED_RW(x));
+	return DATAPTR_RW(WRAPPER_WRAPPED_RW(x));
     else
 	/**** could avoid the cast by having separate methods */
 	return (void *) DATAPTR_RO(WRAPPER_WRAPPED(x));

src/main/memory.c

@@ -4160,6 +4160,9 @@ void *(STDVEC_DATAPTR)(SEXP x)
     return STDVEC_DATAPTR(x);
 }
 
+/* nedded for implementing Dataptr ALTREP methods */
+void *DATAPTR_RW(SEXP x) { return DATAPTR(x); }
+
 int *(LOGICAL)(SEXP x) {
     if(TYPEOF(x) != LGLSXP)
 	error("%s() can only be applied to a '%s', not a '%s'",