Make it a helper

Author: MichaelChirico

src/assign.c

@@ -239,8 +239,7 @@ SEXP setdt_nrows(SEXP x)
       len_xi = INTEGER(dim_xi)[0];
     } else {
       // Be sure to do length() dispatch, #4800
-      len_xi = INTEGER(PROTECT(eval(PROTECT(lang2(install("length"), xi)), R_GlobalEnv)))[0];
-      UNPROTECT(2);
+      len_xi = INTEGER(length_with_dispatch(xi))[0];
     }
     if (!base_length) {
       base_length = len_xi;

src/data.table.h

@@ -350,6 +350,6 @@ SEXP test_dt_win_snprintf(void);
 SEXP dt_zlib_version(void);
 SEXP dt_has_zlib(void);
 SEXP startsWithAny(SEXP, SEXP, SEXP);
+SEXP length_with_dispatch(SEXP);
 SEXP convertDate(SEXP, SEXP);
 SEXP fastmean(SEXP);
-

src/utils.c

@@ -449,6 +449,12 @@ SEXP startsWithAny(const SEXP x, const SEXP y, SEXP start) {
   return ScalarLogical(false);
 }
 
+SEXP length_with_dispatch(SEXP x) {
+  SEXP l = PROTECT(eval(PROTECT(lang2(install("length"), x)), R_GlobalEnv));
+  UNPROTECT(2);
+  return l;
+}
+
 void internal_error(const char *call_name, const char *format, ...) {
   char buff[1024];
   va_list args;