Value Categories and References

Rvalue Bindings

An rvalue reference can bind to a temporary expression so the program can name that temporary result.

rvalue reference An rvalue reference uses `&&` and can bind to a temporary value.
temporary expression Expressions such as arithmetic results do not have stable names until they are bound or stored.

Rvalue Bindings

base
rvalue_bindings.cpp
Replay: real traced execution (multi-file project)
#include <iostream>

int main() {
    int base = 6;

    int&& temporary = base * 2;
    int total = temporary + 1;

    std::cout << "temporary=" << temporary << std::endl;
    std::cout << "total=" << total << std::endl;
    return 0;
}

#include <iostream>

int main() {
    int base = 2;

    int&& temporary = base * 2;
    int total = temporary + 1;

    std::cout << "temporary=" << temporary << std::endl;
    std::cout << "total=" << total << std::endl;
    return 0;
}

#include <iostream>

int main() {
    int base = 10;

    int&& temporary = base * 2;
    int total = temporary + 1;

    std::cout << "temporary=" << temporary << std::endl;
    std::cout << "total=" << total << std::endl;
    return 0;
}

  1. base ← 6, temporary ← 12, total ← 13

    3int main() {4    int base→ 6 = 6; //@base=2, 1056    int&& temporary→ 12 = base6 * 2;7    int total→ 13 = temporary12 + 1;89    std::cout << "temporary=" << temporary12 << std::endl;10    std::cout << "total=" << total13 << std::endl;11    return 0;12}
    outputtemporary=12
total=13

  1. base ← 2, temporary ← 4, total ← 5

    3int main() {4    int base→ 2 = 2;56    int&& temporary→ 4 = base2 * 2;7    int total→ 5 = temporary4 + 1;89    std::cout << "temporary=" << temporary4 << std::endl;10    std::cout << "total=" << total5 << std::endl;11    return 0;12}
    outputtemporary=4
total=5

  1. base ← 10, temporary ← 20, total ← 21

    3int main() {4    int base→ 10 = 10;56    int&& temporary→ 20 = base10 * 2;7    int total→ 21 = temporary20 + 1;89    std::cout << "temporary=" << temporary20 << std::endl;10    std::cout << "total=" << total21 << std::endl;11    return 0;12}
    outputtemporary=20
total=21