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A general description is here.
New functions ‘R_altrep_class_name’ and ‘R_altrep_class_package’ for retrieving the class name symbol and package name symbol of an ALTREP object. These should be used instead of ‘ALTREP_CLASS’.
New function ‘R_getAttributes’ returns the same result as the R function ‘attributes’. New functions ‘R_getAttribCount’, ‘R_getAttribNames’, ‘R_hasAttrib’, ‘R_nrow’, and ‘R_ncol’.
New function ‘DATAPTR_RW()’ for use in implementing ALTREP ‘Dataptr’ methods. This function should not be used in any other contexts.