cpp11 - welding R and C++

R and S have a long history of interacting with compiled languages. The Rcpp package has been a widely successful project, however over the years a number of issues and additional C++ features have arisen. Modifying Rcpp to fix or include these would require a great deal of work, or in some cases would be impossible without severely breaking backwards compatibility. cpp11 is a ground up rewrite of C++ bindings to R with different design trade-offs and features. This talk will focus on the new features of cpp11 including:

- Enforcing copy-on-write semantics.
- Improving the safety of using the R API from C++ code.
- Supporting ALTREP objects.
- Using UTF-8 strings everywhere.
- Applying newer C++11 features.

Transcript

1. cpp11
   welding R and C++
    @jimhester_
   Photo by Christopher Burns on Unsplash
   

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2. C++
   very fast
   statically typed
   lots of libraries
   limited safety net
   Photo by Filipa Saldanha on Unsplash
   

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3. View Slide

4. Then why cpp11?
   Photo by Russ Ward on Unsplash
   

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5. Photo by Micah Tindell on Unsplash
   

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6. C++11
   move semantics
   auto pointers
   type traits
   initializer lists
   variadic templates
   user defined literals
   user defined attributes
   Photo by Markus Spiske on Unsplash
   

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7. # Files Lines of code
   Rcpp (1.0.4) 379 74,658
   cpp11 (1.0.0) 19 1,734
   Simpler implementation
   

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8. Rcpp features not in cpp11
   ❌ No modules
   ❌ No sugar
   ❌ Less attributes
   ❌ No automatic random number restoration
   ❌ No roxygen2 comment documentation
   ❌ No interfaces
   

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9. package
   Rcpp
   compile time
   cpp11
   compile time
   Rcpp
   peak
   memory
   cpp11 peak
   memory
   haven 17.42s 7.13s 428MB 204MB
   readr 124.13s 81.08s 969MB 684MB
   roxygen2 17.34s 4.24s 371MB 109MB
   tidyr 14.25s 3.34s 363MB 83MB
   Cheaper compilation
   

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10. header only
    Install pkgA with Rcpp x.y.z
    Later upgrade Rcpp
    pkgA segfaults
    tidyverse/dplyr#2335
    Photo by Yogendra Singh on Unsplash
    

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11. vendor-able
    bring cpp11 to your
    ensure stability
    (miss out on updates)
    cpp_vendor()
    Photo by Humphrey Muleba on Unsplash
    

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12. Protection cost
    

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13. Vector growth
    

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14. ✅ Semantics
    Safety
    Unicode
    ALTREP
    

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15. –R Language Definition (Version 4.0.3)
    “The semantics of invoking a function in R argument are call-by-value.
    (sic). Changing the value of a supplied argument within a function will
    not affect the value of the variable in the calling frame.”
    

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16. sum_vec <- function(x) {
    sum <- 0
    for (val in x) {
    sum <- sum + val
    }
    sum
    }
    

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17. Rcpp::sourceCpp(code = '#include "Rcpp.h"
    using namespace Rcpp;
    // [[Rcpp::export]]
    int sum_vec_rcpp(IntegerVector x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }')
    

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18. Call-by-value
    x <- 1:3
    sum_vec(x)
    #> [1] 6
    x
    #> [1] 1 2 3
    sum_vec_rcpp(x)
    #> [1] 6
    x
    #> [1] 1 2 3
    

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19. add_first <- function(x) {
    x[[1]] <- x[[1]] + 1
    x
    }
    Call-by-value
    

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20. Rcpp::sourceCpp(code = '#include "Rcpp.h"
    using namespace Rcpp;
    // [[Rcpp::export]]
    IntegerVector add_first_rcpp(IntegerVector x) {
    x[0] = x[0] + 1;
    return x;
    }')
    Call-by-value?
    

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21. x <- 1:3
    add_first(x)
    #> [1] 2 2 3
    x
    #> [1] 1 2 3
    add_first_rcpp(x)
    #> [1] 2 2 3
    x
    #> [1] 2 2 3
    Call-by-reference
    

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22. x <- 1:3
    add_first(x)
    #> [1] 2 2 3
    x
    #> [1] 1 2 3
    add_first_rcpp(x)
    #> [1] 2 2 3
    x
    #> [1] 2 2 3
    Call-by-reference
    

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23. Rcpp::sourceCpp(code = '#include "Rcpp.h"
    using namespace Rcpp;
    // [[Rcpp::export]]
    IntegerVector add_first_rcpp(IntegerVector x) {
    x[0] = x[0] + 1;
    return x;
    }')
    Call-by-reference
    

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24. Rcpp::sourceCpp(code = '#include "Rcpp.h"
    using namespace Rcpp;
    // [[Rcpp::export]]
    IntegerVector add_first_rcpp(IntegerVector x) {
    x[0] = x[0] + 1;
    return x;
    }')
    Call-by-reference
    

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25. Pinnacle
    of success
    Photo by lovely shots on Unsplash
    

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26. Pit of success
    Photo by Eric Muhr on Unsplash
    

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27. cpp11::cpp_function(code = '
    int sum_vec_cpp11(integers x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    [[cpp11::register]]
    integers add_one_cpp11(writable::integers x) {
    x[0] = x[0] + 1;
    return x;
    }
    ')
    

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28. cpp11::cpp_function(code = '
    int sum_vec_cpp11(integers x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    [[cpp11::register]]
    integers add_one_cpp11(writable::integers x) {
    x[0] = x[0] + 1;
    return x;
    }
    ')
    

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29. cpp11::cpp_function(code = '
    int sum_vec_cpp11(integers x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    [[cpp11::register]]
    integers add_one_cpp11(writable::integers x) {
    x[0] = x[0] + 1;
    return x;
    }
    ')
    

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30. cpp11::cpp_function(code = '
    integers add_one_cpp11(integers x) {
    x[0] = x[0] + 1;
    return x;
    }', quiet = FALSE)
    // error: expression is not assignable
    // x[0] = x[0] + 1;
    // ~~~~ ^
    

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31. Call-by-value
    x <- 1:3
    sum_vec_cpp11(x)
    #> [1] 6
    x
    #> [1] 1 2 3
    add_one_cpp11(x)
    #> [1] 2 2 3
    x
    #> [1] 1 2 3
    

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32. Call-by-value
    x <- 1:3
    sum_vec_cpp11(x)
    #> [1] 6
    x
    #> [1] 1 2 3
    add_one_cpp11(x)
    #> [1] 2 2 3
    x
    #> [1] 1 2 3
    

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33. Safety
    Photo by Rob Lambert on Unsplash
    

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34. void fun() {
    std::string str("foo");
    Rf_error("something went wrong");
    }
    Memory leak?
    

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35. void fun() {
    char* str = (char*) malloc(1024);
    Rf_error("something went wrong");
    free(str);
    }
    Memory leak
    

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36. void fun() {
    std::string str("foo");
    throw std::runtime_error("something went wrong");
    }
    No memory leak
    

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37. Rcpp::sourceCpp(code = '#include "Rcpp.h"
    std::string fun() {
    std::string str("foo");
    return str;
    }')
    Memory leak
    

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38. SEXP fun() {
    std::string str("foo");
    SEXP x = Rf_allocVector(STRSXP, 1);
    SET_STRING_ELT(x, 0, Rf_mkChar(str.c_str()));
    return x
    }
    Safety
    Memory leak
    

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39. SEXP fun() {
    std::string str("foo");
    SEXP x = Rf_allocVector(STRSXP, 1);
    SET_STRING_ELT(x, 0, Rf_mkChar(str.c_str()));
    return x
    }
    Safety
    Memory leak
    

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40. SEXP fun() {
    std::string str("foo");
    SEXP x = Rf_allocVector(STRSXP, 1);
    SET_STRING_ELT(x, 0, Rf_mkChar(str.c_str()));
    return x
    }
    Safety
    Memory leak
    

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41. –Jim Hester
    “All calls to R API functions can potentially error.”
    

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42. Pit of success
    Photo by Kelly Sikkema on Unsplash
    

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43. SEXP fun() {
    std::string str("foo");
    cpp11::unwind_protect([&] {
    SEXP x = Rf_allocVector(STRSXP, 1);
    SET_STRING_ELT(x, 0, Rf_mkChar(str.c_str()));
    });
    return x
    }
    No memory leak
    

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44. SEXP fun() {
    std::string str("foo");
    cpp11::unwind_protect([&] {
    SEXP x = Rf_allocVector(STRSXP, 1);
    SET_STRING_ELT(x, 0, Rf_mkChar(str.c_str()));
    });
    return x
    }
    No memory leak
    

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45. SEXP fun() {
    std::string str("foo");
    SEXP x = cpp11::safe[Rf_allocVector](STRSXP, 1);
    SET_STRING_ELT(x, 0, cpp11::safe[Rf_mkChar](str.c_str()));
    return x
    }
    No memory leak
    

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46. SEXP fun() {
    std::string str("foo");
    SEXP x = cpp11::safe[Rf_allocVector](STRSXP, 1);
    SET_STRING_ELT(x, 0, cpp11::safe[Rf_mkChar](str.c_str()));
    return x
    }
    No memory leak
    

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47. SEXP fun() {
    std::string str("foo");
    SEXP x = cpp11::safe[Rf_allocVector](STRSXP, 1);
    SET_STRING_ELT(x, 0, cpp11::safe[Rf_mkChar](str.c_str()));
    return x
    }
    No memory leak
    

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48. Unicode
    Photo by Henry & Co. on Unsplash
    

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49. Getting unicode right is HARD!
    

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50. Getting unicode right is HARD!
    

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51. Getting unicode right is HARD!
    

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52. Getting unicode right is HARD!
    

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53. Rcpp::sourceCpp(code = '
    #include "Rcpp.h"
    // [[Rcpp::export]]
    std::string do_nothing_rcpp(std::string x) {
    return x;
    }')
    

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54. x <- "fa\xE7ile"
    Encoding(x) <- "latin1"
    do_nothing_rcpp(x)
    #> [1] "façile"
    

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55. x <- "fa\U00E7ile"
    do_nothing_rcpp(x)
    #> [1] "façile"
    

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56. Pit of success
    Photo by Tim Gouw on Unsplash
    

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57. - utf8everywhere.org, Pavel Radzivilovsky, Yakov Galka and Slava Novgorodov
    “(UTF-8) should be the default choice of encoding for storing text
    strings in memory or on disk, for communication and all other uses.
    (this) improves performance, reduces complexity of software and helps
    prevent many Unicode-related bugs.”
    

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58. – https://cpp11.r-lib.org/articles/motivations.html
    “text coming from R is always translated into UTF-8.
    text coming from C++ is always marked as UTF-8."
    

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59. cpp11::cpp_source(code = '
    #include
    [[cpp11::register]]
    std::string do_nothing_cpp(std::string x) {
    return x;
    }')
    

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60. SEXP f(SEXP x) {
    std::string str;
    str.reserve(Rf_xlength(STRING_ELT(x, 0)));
    void* vmax = vmaxget();
    str.assign(Rf_translateCharUTF8(STRING_ELT(x, 0)));
    vmaxset(vmax);
    api.do_stuff(str);
    }
    To C++
    

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61. From C++
    SEXP f(SEXP x) {
    std::string data = api.get_data();
    return Rf_ScalarString(Rf_mkCharLenCE(data.c_str(),
    data.size(), CE_UTF8));
    }
    

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62. x <- "fa\xE7ile"
    Encoding(x) <- "latin1"
    do_nothing_cpp(x)
    #> [1] "façile"
    

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63. x <- "fa\U00E7ile"
    do_nothing_cpp(x)
    #> [1] "façile"
    

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64. ALTREP
    Alternative representation
    R 3.5+
    Where's the data?
    Used in base R
    Used in
    Photo by Danilo Santos on Unsplash
    

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66. ALTREP aware
    sum_vec <- function(x) {
    sum <- 0
    for (val in x) {
    sum <- sum + val
    }
    sum
    }
    x <- 1:10000
    sum_vec(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @105a00cf8 13 INTSXP g0c0
    [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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67. ALTREP aware
    sum_vec <- function(x) {
    sum <- 0
    for (val in x) {
    sum <- sum + val
    }
    sum
    }
    x <- 1:10000
    sum_vec(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @105a00cf8 13 INTSXP g0c0
    [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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68. ALTREP aware
    sum_vec <- function(x) {
    sum <- 0
    for (val in x) {
    sum <- sum + val
    }
    sum
    }
    x <- 1:10000
    sum_vec(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @105a00cf8 13 INTSXP g0c0
    [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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69. Not ALTREP aware
    // [[Rcpp::export]]
    int sum_vec_rcpp(IntegerVector x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    x <- 1:10000
    sum_vec_rcpp(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @10600fe40 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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70. Not ALTREP aware
    // [[Rcpp::export]]
    int sum_vec_rcpp(IntegerVector x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    x <- 1:10000
    sum_vec_rcpp(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @10600fe40 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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71. Not ALTREP aware
    // [[Rcpp::export]]
    int sum_vec_rcpp(IntegerVector x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    x <- 1:10000
    sum_vec_rcpp(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @10600fe40 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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72. Not ALTREP aware
    // [[Rcpp::export]]
    int sum_vec_rcpp(IntegerVector x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    x <- 1:10000
    sum_vec_rcpp(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @10600fe40 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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73. Not ALTREP aware
    SEXP sum_vec_c(SEXP x) {
    int sum = 0;
    int* p = INTEGER(x);
    for (R_xlen_t i = 0; i < Rf_xlength(x); ++i) {
    sum = sum + p[i];
    }
    return Rf_ScalarInteger(sum);
    }
    x <- 1:10000
    sum_vec_c(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1351f7858 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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74. Not ALTREP aware
    SEXP sum_vec_c(SEXP x) {
    int sum = 0;
    int* p = INTEGER(x);
    for (R_xlen_t i = 0; i < Rf_xlength(x); ++i) {
    sum = sum + p[i];
    }
    return Rf_ScalarInteger(sum);
    }
    x <- 1:10000
    sum_vec_c(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1351f7858 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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75. Not ALTREP aware
    SEXP sum_vec_c(SEXP x) {
    int sum = 0;
    int* p = INTEGER(x);
    for (R_xlen_t i = 0; i < Rf_xlength(x); ++i) {
    sum = sum + p[i];
    }
    return Rf_ScalarInteger(sum);
    }
    x <- 1:10000
    sum_vec_c(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1351f7858 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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76. Not ALTREP aware
    SEXP sum_vec_c(SEXP x) {
    int sum = 0;
    int* p = INTEGER(x);
    for (R_xlen_t i = 0; i < Rf_xlength(x); ++i) {
    sum = sum + p[i];
    }
    return Rf_ScalarInteger(sum);
    }
    x <- 1:10000
    sum_vec_c(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1351f7858 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (expanded)
    lobstr::obj_sizes(x)
    #> 40,728 B
    

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77. ALTREP aware
    SEXP sum_vec_c2(SEXP x) {
    int sum = 0;
    for (R_xlen_t i = 0; i < Rf_xlength(x); ++i) {
    sum = sum + INTEGER_ELT(x, i);
    }
    return Rf_ScalarInteger(sum);
    }
    x <- 1:10000
    sum_vec_c2(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @103e50f80 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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78. ALTREP aware
    SEXP sum_vec_c2(SEXP x) {
    int sum = 0;
    for (R_xlen_t i = 0; i < Rf_xlength(x); ++i) {
    sum = sum + INTEGER_ELT(x, i);
    }
    return Rf_ScalarInteger(sum);
    }
    x <- 1:10000
    sum_vec_c2(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @103e50f80 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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79. ALTREP aware
    SEXP sum_vec_c2(SEXP x) {
    int sum = 0;
    for (R_xlen_t i = 0; i < Rf_xlength(x); ++i) {
    sum = sum + INTEGER_ELT(x, i);
    }
    return Rf_ScalarInteger(sum);
    }
    x <- 1:10000
    sum_vec_c2(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @103e50f80 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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80. ALTREP aware
    SEXP sum_vec_c3(SEXP x) {
    int sum = 0;
    int buf[1024];
    R_xlen_t i = 0;
    R_xlen_t n = Rf_xlength(x);
    while(i < n - 1024) {
    INTEGER_GET_REGION(x, i, 1024, buf);
    for (R_xlen_t j = 0; j < 1024; ++j) {
    sum = sum + buf[j];
    }
    i += 1024;
    }
    R_xlen_t extra = n - i;
    INTEGER_GET_REGION(x, i, extra, buf);
    for (R_xlen_t j = 0; j < extra; ++j) {
    sum = sum + buf[j];
    }
    return Rf_ScalarInteger(sum);
    }
    }
    x <- 1:10000
    sum_vec_c3(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1342a4be0 13 INTSXP g0c0
    #> [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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81. ALTREP aware
    SEXP sum_vec_c3(SEXP x) {
    int sum = 0;
    int buf[1024];
    R_xlen_t i = 0;
    R_xlen_t n = Rf_xlength(x);
    while(i < n - 1024) {
    INTEGER_GET_REGION(x, i, 1024, buf);
    for (R_xlen_t j = 0; j < 1024; ++j) {
    sum = sum + buf[j];
    }
    i += 1024;
    }
    R_xlen_t extra = n - i;
    INTEGER_GET_REGION(x, i, extra, buf);
    for (R_xlen_t j = 0; j < extra; ++j) {
    sum = sum + buf[j];
    }
    return Rf_ScalarInteger(sum);
    }
    }
    x <- 1:10000
    sum_vec_c3(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1342a4be0 13 INTSXP g0c0
    #> [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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82. ALTREP aware
    SEXP sum_vec_c3(SEXP x) {
    int sum = 0;
    int buf[1024];
    R_xlen_t i = 0;
    R_xlen_t n = Rf_xlength(x);
    while(i < n - 1024) {
    INTEGER_GET_REGION(x, i, 1024, buf);
    for (R_xlen_t j = 0; j < 1024; ++j) {
    sum = sum + buf[j];
    }
    i += 1024;
    }
    R_xlen_t extra = n - i;
    INTEGER_GET_REGION(x, i, extra, buf);
    for (R_xlen_t j = 0; j < extra; ++j) {
    sum = sum + buf[j];
    }
    return Rf_ScalarInteger(sum);
    }
    }
    x <- 1:10000
    sum_vec_c3(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1342a4be0 13 INTSXP g0c0
    #> [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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83. ALTREP aware
    SEXP sum_vec_c3(SEXP x) {
    int sum = 0;
    int buf[1024];
    R_xlen_t i = 0;
    R_xlen_t n = Rf_xlength(x);
    while(i < n - 1024) {
    INTEGER_GET_REGION(x, i, 1024, buf);
    for (R_xlen_t j = 0; j < 1024; ++j) {
    sum = sum + buf[j];
    }
    i += 1024;
    }
    R_xlen_t extra = n - i;
    INTEGER_GET_REGION(x, i, extra, buf);
    for (R_xlen_t j = 0; j < extra; ++j) {
    sum = sum + buf[j];
    }
    return Rf_ScalarInteger(sum);
    }
    }
    x <- 1:10000
    sum_vec_c3(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @1342a4be0 13 INTSXP g0c0
    #> [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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84. function time
    sum_vec_c 374µs
    sum_vec_c2 625µs
    sum_vec_c3 186µs
    

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85. Pit of success
    Photo by Christian Bowen on Unsplash
    

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86. ALTREP aware
    int sum_vec_cpp11(integers x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    x <- 1:10000
    sum_vec_cpp11(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @134b695f0 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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87. ALTREP aware
    int sum_vec_cpp11(integers x) {
    int sum = 0;
    for (auto val : x) {
    sum = sum + val;
    }
    return sum;
    }
    x <- 1:10000
    sum_vec_cpp11(x)
    #> [1] 50005000
    .Internal(inspect(x))
    #> @134b695f0 13 INTSXP g0c0 [REF(65535)] 1 : 10000 (compact)
    lobstr::obj_sizes(x)
    #> 680 B
    

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88. ✅ Semantics
    Safety
    Unicode
    ALTREP
    cpp11.r-lib.org
    C++11
    simple(r)
    cheaper
    | compilation
    | appending
    | protection
    header only
    vendor-able
     @jimhester_
    

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