C++ vs Rust

[Paul Lopez]

Think it's useful at all combined with a state machine or chain of responsibility pattern? Seems clunky.

 

[Daniel Duffy]

Think it's useful at all combined with a state machine or chain of responsibility pattern? Seems clunky.

It all seems less elegant than others. just a random remark.

 

[Paul Lopez]

It all seems less elegant than others. just a random remark.

But a very poignant one coming from someone with your experience and knowledge I say! They have work to do.

 

[Paul Lopez]

Getting this to interop with some python and/or Golang APIs and a C/C++ analytical library...just not seeing it be too clean yet.

 

[MichaelLewis]

The following code uses features from C++20 and QN Adv C++ course that uses Concepts
// At this moment I have a vague idea on how I would do it in Rust; is it even worth the effort..

@APalley
@MichaelLewis

// Test101ActorConcepts.cpp
//
// Simplest example of a system. Context diagram consists only
// of Input and Output systems.
//
// We use C++20 Concepts to replace V1 (outdated) policy-based design (PBD)
//
// Composition
//
//  V2: design using C++20 Concepts
//  V3: V2 + embedded actors
//
// Problem now becomes a pipeline Source -> SUD -> Sink
//
// Summary: this approach is feasible, so worth investigating..
// 1992 .. everything is an object
// 2024 .. everything is an actor
//
// (C) Datasim Education BV 2015-2024
//

#include <string>
#include <iostream>
#include <type_traits>
#include <mutex>
#include <agents.h>

// Interface contract specification
// 1. Each concept is an abstract method
// 2. interface == concept conjunction (e.g. ISUD)

// 1. Define abstract methods (building blocks)
template<typename Message, template <typename Message> class T> // abstract method
    concept ISource = requires (T<Message> x) { x.message(); };
template<typename Message, template <typename Message> class T> // abstract method
    concept ISink = requires (T<Message> x, const Message& s) { x.print(s); };

// 2. Interface relating to context diagram; cojunctional concepts are an alternative
// to multiple inheritance but no danger of fragile base class problem
template< typename Message, template<typename Message> class Input, template<typename Message> class Output>
    concept ISUD = ISource<Message, Input> && ISink<Message, Output>;

// Agent actor-based constraints
template<typename Derived>
    concept IActor1 = std::derived_from<Derived, concurrency::agent>;
template<typename T>
    concept IActor2 = requires (T x) { x.run(); };

// 3. Interface relating to defining constraints pertaining to Actor technology
// https://learn.microsoft.com/en-us/cpp/parallel/concrt/asynchronous-agents-library?view=msvc-170
template<typename Derived>
    concept IActor = IActor1<Derived> && IActor2<Derived>;
  
// The mediator using template template parameter "trick" => can use generic messages
template <typename Message, template <typename Message> class Source, template <typename Message> class Sink>
                requires ISUD<Message, Source, Sink> &&  IActor<Source<Message>> && IActor<Sink<Message>>
    class SUD : public concurrency::agent
{ // SUD is in a chain from Input to Output

private:
    concurrency::ISource<Message>& _source; // formerly known as src
    concurrency::ITarget<Message>& _target; // formerly known as snk
public:
    explicit SUD(concurrency::ISource<Message>& source, concurrency::ITarget<Message>& target)
        : _source(source), _target(target) {}

    void run()
    {
        Message info = concurrency::receive(_source);
        concurrency::send(_target, info);

        done();
    }
};   

// Instance Systems
template <typename Message>
    class MySource : public concurrency::agent
{
    concurrency::ITarget<Message>& _target; // send to SUD
    Message _msg;
public:
    explicit MySource(const Message& msg, concurrency::ITarget<Message>& target)
        : _target(target), _msg(msg) {}

    Message message() const
    {
        // Get data from hardware device
        return Message(_msg);
    }

    void run()
    {
        concurrency::send(_target, message());

        done();
    }

};

template <typename Message>
    class MySink : public concurrency::agent
{
    concurrency::ISource<Message>& _source; // received from SUD
    int _id;
    Message info;
    std::mutex myMutex;
public:
    explicit MySink(concurrency::ISource<Message>& source, int ID = 0) : _source(source), _id(ID) {}
    void print(const Message& s)
    {
        std::lock_guard<std::mutex> guard(myMutex);
        std::cout << "\nin a sink: " << _id << ": " << info << std::endl;
    }

    void run()
    {
        info = concurrency::receive(_source);
        print(info);
        done();
    }

    double compute(int val)
    {
        info *= val*_id;
        return info;
    }
};

int main()
{
    { // Single sink
        using Message = std::string;
        Message m(" good morning");

        // All actors access (read from/write to) a single buffer
        concurrency::overwrite_buffer<Message> buffer;
        MySource i(m, buffer);
        SUD<Message, MySource, MySink> s(buffer, buffer);
        MySink o(buffer);

        i.start(); o.start(); s.start();
        concurrency::agent::wait(&i); concurrency::agent::wait(&s); concurrency::agent::wait(&o);
    }

    {    // Multiple sinks
        using Message = int;
        Message m(23);

        // All actors access (read from/write to) a single buffer
        concurrency::overwrite_buffer<Message> buffer;
        MySource i(m, buffer);
        SUD<Message, MySource, MySink> s(buffer, buffer);
        MySink o1(buffer, 1);
        MySink o2(buffer, 2);
        MySink o3(buffer, 3);
        i.start(); s.start();
        o1.start(); o2.start(); o3.start();
        concurrency::agent::wait(&i); concurrency::agent::wait(&s);
        concurrency::agent::wait(&o1);
        concurrency::agent::wait(&o2);
        concurrency::agent::wait(&o3);

        std::cout << "\ncompute: " << o1.compute(2) << '\n';
        std::cout << "\ncompute: " << o2.compute(2) << '\n';
        std::cout << "\ncompute: " << o3.compute(2) << '\n';
    }

    return 0;
}

I’d be interested in seeing the Rust version.

It seems like most in this thread don’t see Rust as a C++ replacement. But I’d still like to see some comparable programs to make the decision a bit more concrete.

 

[Daniel Duffy]

I’d be interested in seeing the Rust version.

It seems like most in this thread don’t see Rust as a C++ replacement. But I’d still like to see some comparable programs to make the decision a bit more concrete.

I understand.
Have you tried some examples in Rust?

 

[Daniel Duffy]

This looks interesting

Memory Thinking for Rust | Software Diagnostics Technology and Services

www.patterndiagnostics.com

 

[Daniel Duffy]

Just out of curiosity, I would be interested in technical (not idiosyncratic, altho' they exist as well) reasons for choosing Rust. I have 35 years C++ exposure and I learned essential Rust in about 5 days. In a sense it is an extreme mini C++.

Channels have potential but they are nowhere near a decent Actor framework IMO.
Maybe the reason: if you are not comfortable with C++, then it might be an option. But its support for OOP and generics is a culture shock. In fairness, it has traits, but then so has C++20 Concepts and more.

I have not seen much on C++ language and Boost library interop.

I could be wrong but at this moment (1st impressions) Rust is a (low-level) systems language. It is unclear to me how it models higher-level abstractions etc.

 

[MichaelLewis]

Just out of curiosity, I would be interested in technical (not idiosyncratic, altho' they exist as well) reasons for choosing Rust. I have 35 years C++ exposure and I learned essential Rust in about 5 days. In a sense it is an extreme mini C++.

Channels have potential but they are nowhere near a decent Actor framework IMO.
Maybe the reason: if you are not comfortable with C++, then it might be an option. But its support for OOP and generics is a culture shock. In fairness, it has traits, but then so has C++20 Concepts and more.

I have not seen much on C++ language and Boost library interop.

I could be wrong but at this moment (1st impressions) Rust is a (low-level) systems language. It is unclear to me how it models higher-level abstractions etc.

I’ve never really done systems programming so I can be wrong, but based on your statement, it sounds as though it’s more akin to a C replacement than a C++ one.

 

[Paul Lopez]

I’ve never really done systems programming so I can be very wrong in this statement, but based on your statement, it sounds as though it’s more akin to a C replacement than a C++ one.

I'd agree there. We are using it as an essential C replacement for now. Maybe folks will give it a go to create an analytical library with it, but it won't replace C++ in that regard in finance land. Certainly not for many many more decades I'd say.

 

[Daniel Duffy]

I’ve never really done systems programming so I can be wrong, but based on your statement, it sounds as though it’s more akin to a C replacement than a C++ one.

Feels a bit like that.
Analogy? If a house were built using different languages, then we get a Rust programmer to do the (low-level) plumbing work.
C might be >> Rust?