Boost Functional Programming

Function

boost::function is the predecessor of std::function — a type-erasing wrapper for callable objects. C++11 standardized it directly.

Signals2: Thread-Safe Signal-Slot

boost::signals2::signal<void(int)> on_value_changed;

// 连接槽
on_value_changed.connect([](int v) { std::cout << "New: " << v; });
on_value_changed.connect([](int v) { log(v); });

// 发射信号
on_value_changed(42);  // 所有连接的槽被调用

Thread-safe: Uses a read-write lock to protect the signal's connection/disconnection list. A shared lock is used during emission (allowing concurrent reads), and an exclusive lock is used for connect/disconnect operations.

Automatic connection management: Use track() to monitor object lifetime; connections are automatically severed when the tracked object is destroyed.

Outcome: Result/Error Type

Boost.Outcome is the predecessor of std::expected, providing three result types:

• result<T, EC>: value or error code (no exceptions)
• outcome<T, EC, EP>: value, error code, or exception
• BOOST_OUTCOME_TRY: error propagation macro

outcome::result<int> parse(std::string_view s) {
    // ...
    if (error) return outcome::failure(std::errc::invalid_argument);
    return 42;
}

auto val = BOOST_OUTTRY(parse("42"));  // 失败时自动返回

Bind and Lambda

boost::bind and boost::lambda are predecessors of C++11 lambdas. Modern projects should use C++11 lambdas directly.