C++ “no match for operator=“ error in lambda function

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• How can I simplify my code? (A simple Fraction class)

  My code seems to work fine. However, I feel like it is a bit too long; I really want to create simple yet efficient codes (they should be readable as well). Any suggestions from you guys would mean a lot to me. Many thanks!

  Sample run: https://i.stack.imgur.com/cnT9A.png

  Here is the fraction.h file:

  #ifndef FRACTION_H 
  #define FRACTION_H
  #include <QString>
  
  class Fraction {
  
  public:
      Fraction();
      Fraction(int numberator, int denominator);
      void set(int numberator, int denominator);
      QString toString();
      double toDouble();
      int findGCD(int a, int b);
      Fraction simplify();
      Fraction add(const Fraction& other);
      Fraction substract(const Fraction& other);
      Fraction multiphy(const Fraction& other);
      Fraction divide(const Fraction& other);
  
  private:
     int m_Numerator;
     int m_Denominator;
  };
  
  #endif // FRACTION_H
  

  Here is the fraction.cpp file:

  #include "fraction.h"
  
  // Constructors:
  Fraction::Fraction()
     :m_Numerator(0), m_Denominator(0) {}
  
  Fraction::Fraction(int numerator, int denominator)
     :m_Numerator(numerator), m_Denominator(denominator) {
  }
  
  // Setter method
  void Fraction::set(int numberator, int denominator) {
      m_Numerator = numberator;
      m_Denominator = denominator;
  }
  
  // GCD
  int Fraction::findGCD(int a, int b) {
      if (a == 0) {
          return b;
      }
      return findGCD(b%a, a);
  }
  
  // Simplify
  Fraction Fraction::simplify() {
      int gcd = findGCD(m_Numerator, m_Denominator);
      return Fraction::Fraction(m_Numerator / gcd, m_Denominator / gcd);
  }
  
  double Fraction::toDouble() {
      return ((double) m_Numerator/m_Denominator);
  }
  
  QString Fraction::toString() {
      return QString("%1 / %2 = %3")
          .arg(m_Numerator)
          .arg(m_Denominator)
          .arg(toDouble());
  }
  
  Fraction Fraction::add(const Fraction &other) {
      int numeratorTemp(m_Numerator);
      int denominatorTemp(m_Denominator);
  
      if (m_Denominator == other.m_Denominator) {
          numeratorTemp = m_Numerator + other.m_Numerator;
      } else {
          numeratorTemp = m_Numerator * other.m_Denominator + other.m_Numerator * m_Denominator;
          denominatorTemp = m_Denominator * other.m_Denominator;
      }
      return Fraction::Fraction(numeratorTemp, denominatorTemp);
  }
  
  Fraction Fraction::substract(const Fraction &other) {
      int numeratorTemp(m_Numerator);
      int denominatorTemp(m_Denominator);
  
      if (m_Denominator == other.m_Denominator) {
          numeratorTemp = m_Numerator - other.m_Numerator;
      } else {
          numeratorTemp = m_Numerator * other.m_Denominator - other.m_Numerator * m_Denominator;
          denominatorTemp = m_Denominator * other.m_Denominator;
      }
      return Fraction::Fraction(numeratorTemp, denominatorTemp);
  }
  
  Fraction Fraction::divide(const Fraction &other) {
      int numeratorTemp(m_Numerator);
      int denominatorTemp(m_Denominator);
  
      numeratorTemp = m_Numerator * other.m_Denominator;
      denominatorTemp = m_Denominator * other.m_Numerator;
      return Fraction::Fraction(numeratorTemp, denominatorTemp);
  }
  
  Fraction Fraction::multiphy(const Fraction &other) {
      int numeratorTemp(m_Numerator);
      int denominatorTemp(m_Denominator);
  
      numeratorTemp  = m_Numerator * other.m_Numerator;
      denominatorTemp = m_Denominator * other.m_Denominator;
      return Fraction::Fraction(numeratorTemp, denominatorTemp);
  }
  

  Main.cpp:

  #include <QCoreApplication>
  #include <iostream>
  #include "fraction.h"
  
  int main()
  {
      using namespace std;
  
      int num1 = 1;
      int denom1 = 2;
  
      int num2 = 5;
      int denom2 = 2;
  
      Fraction frac1(num1, denom1);
      Fraction frac2(num2, denom2);
  
      cout << "Addition: 1/2 + 5/2 = " << frac1.add(frac2).simplify().toString().toUtf8().constData() << endl;
      cout << "Substraction: 1/2 - 5/2 = " << frac1.substract(frac2).simplify().toString().toUtf8().constData() << endl;
      cout << "Divide: 1/2 : 5/2 = " << frac1.divide(frac2).simplify().toString().toUtf8().constData() << endl;
      cout << "Multiplication: 1/2 * 5/2 = " << frac1.multiphy(frac2).simplify().toString().toUtf8().constData() << endl;
  
  }
  

  Output: https://i.stack.imgur.com/cnT9A.png
• Why do I have to set the error state flag to goodbit in order for this to work?

  #include <iostream>
  #include <fstream>
  #include <string>
  
  int main()
  {
      std::ofstream os("test.txt");
      std::ifstream is("test.txt");
      std::string value("0");
  
      os << "Hello";
      is >> value;
  
      std::cout << "Result before tie(): \"" << value << "\"\n";
      is.clear();
      is.tie(&os);
  
      is >> value;
  
      std::cout << "Result after tie(): \"" << value << "\"\n";
  }
  

  The above code has the output:

  Result before tie(): "0"
  Result after tie(): "Hello"
  

  But without the clear() call, value stays "0" - why? Why do I have to set the error state flag of the input stream to goodbit?

  Note that the file cannot be found, which is the intention.
• How to handle situation of loading wrong shared library version

  I am facing with strange situation. My engine is supposed to call some function of another library. Problems is if I can have wrong (incompatible) library package version in the system, engine will stop working without any exception or Linux signal. Basically, engine is handling basic Linux signals as segmentation fault etc. These signals will not come. My program is looking like:

  try {
      interface->somefunctioncall(...);
  } catch(...) {
      ;
  }
  

  interface->somefunctioncall(...) is call to another shared library from another package. If package has wrong version, this call will cause to crash engine and there will be no information in Linux system about it. I want only to handle this situation somehow and store some information to the log. Whatever will happen. Engine can crash. But I want to have stored information in log why engine crashed. Another nice hint could be, if I can handle this situation in run time and engine could continue. Make sure that I am developing on embedded Linux with limited possibilities to use third - parties software. Please no hints like:

  if (packageversion != expectedversion) {
      do_not_do_call_and_log_the_problem();
  } else {
      interface->somefunctioncall(...);
  }
  

  Thanks a lot for hints. :-)
• Why does Java lamda reflection performance get worse

  I have constructed a simple test to measure the performance of class reflection with the Java LambdaMetafactory. According to various posts reflection using LambdaMetafactory is as fast as directly calling getters. This seems true initially, but after a while performance degrades.

  One of the test shows (this seems general trend):

  Initially:

  GET - REFLECTION: Runtime=2.841seconds
  GET - DIRECT:     Runtime=0.358seconds
  GET - LAMBDA:     Runtime=0.362seconds
  SET - REFLECTION: Runtime=3.86seconds
  SET - DIRECT:     Runtime=0.507seconds
  SET - LAMBDA:     Runtime=0.455seconds
  

  Finally:

  GET - REFLECTION: Runtime=2.904seconds
  GET - DIRECT:     Runtime=0.501seconds
  GET - LAMBDA:     Runtime=5.299seconds
  SET - REFLECTION: Runtime=4.62seconds
  SET - DIRECT:     Runtime=1.723seconds
  SET - LAMBDA:     Runtime=5.149seconds
  

  Code follows below.

  Questions:

  • Why?

  • How can this be made more performant with the LambdaMetafactory?

  ---

  package lambda;
  
  public class Main {
  
      public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, Throwable {
          int runs = 5;
  
          for (int i = 0; i < runs; i++) {
              System.out.println("***** RUN " + i);
  
              Lambda lam = new Lambda();
              lam.initGetter(Person.class, "getName");
              lam.initSetter(Person.class, "setSalary", double.class);
  
              Test test = new Test();
              test.doTest(lam);
          }
  
      }
  }
  

  ---

  package lambda;
  
  import java.lang.invoke.CallSite;
  import java.lang.invoke.LambdaMetafactory;
  import java.lang.invoke.MethodHandle;
  import java.lang.invoke.MethodHandles;
  import java.lang.invoke.MethodType;
  import java.lang.reflect.Method;
  import java.util.function.BiConsumer;
  import java.util.function.Function;
  
  public final class Lambda {
  
      //https://www.optaplanner.org/blog/2018/01/09/JavaReflectionButMuchFaster.html
      //https://bytex.solutions/2017/07/java-lambdas/
      //https://stackoverflow.com/questions/27602758/java-access-bean-methods-with-lambdametafactory
      private Function getterFunction;
      private BiConsumer setterFunction;
  
      private Function createGetter(final MethodHandles.Lookup lookup,
              final MethodHandle getter) throws Exception {
          final CallSite site = LambdaMetafactory.metafactory(lookup, "apply",
                  MethodType.methodType(Function.class),
                  MethodType.methodType(Object.class, Object.class), //signature of method Function.apply after type erasure
                  getter,
                  getter.type()); //actual signature of getter
          try {
              return (Function) site.getTarget().invokeExact();
          } catch (final Exception e) {
              throw e;
          } catch (final Throwable e) {
              throw new Exception(e);
          }
      }
  
      private BiConsumer createSetter(final MethodHandles.Lookup lookup,
              final MethodHandle setter) throws Exception {
          final CallSite site = LambdaMetafactory.metafactory(lookup,
                  "accept",
                  MethodType.methodType(BiConsumer.class),
                  MethodType.methodType(void.class, Object.class, Object.class), //signature of method BiConsumer.accept after type erasure
                  setter,
                  setter.type()); //actual signature of setter
          try {
              return (BiConsumer) site.getTarget().invokeExact();
          } catch (final Exception e) {
              throw e;
          } catch (final Throwable e) {
              throw new Exception(e);
          }
      }
  
      public void initGetter(Class theSubject, String methodName) throws ReflectiveOperationException, Exception {
          MethodHandles.Lookup lookup = MethodHandles.lookup();
          Method m = theSubject.getMethod(methodName);
          MethodHandle mh = lookup.unreflect(m);
  
          getterFunction = createGetter(lookup, mh);
      }
  
      public void initSetter(Class theSubject, String methodName, Class parameterType) throws ReflectiveOperationException, Exception {
          MethodHandles.Lookup lookup = MethodHandles.lookup();
          Method m = theSubject.getMethod(methodName, parameterType);
          MethodHandle mh = lookup.unreflect(m);
  
          setterFunction = createSetter(lookup, mh);
      }
  
      public Object executeGetter(Object theObject) {
          return getterFunction.apply(theObject);
      }
  
      public void executeSetter(Object theObject, Object value) {
          setterFunction.accept(theObject, value);
      }
  
  }
  

  ---

  package lambda;
  
  import java.lang.reflect.Field;
  
  public class Test {
  
      public void doTest(Lambda lam) throws NoSuchFieldException, IllegalArgumentException, Exception {
  
          if (lam == null) {
              lam = new Lambda();
              lam.initGetter(Person.class, "getName");
              lam.initSetter(Person.class, "setSalary", double.class);
          }
  
          Person p = new Person();
          p.setName(111);
  
          long loops = 1000000000; // 10e9
          System.out.println("Loops: " + loops);
  
          ///
          System.out.println("GET - REFLECTION:");
  
          Field field = Person.class.getField("name");
  
          long start = System.currentTimeMillis();
          for (int i = 0; i < loops; i++) {
              int name = (int) field.get(p);
          }
          long end = System.currentTimeMillis();
          System.out.println("Runtime=" + ((end - start) / 1000.0) + "seconds");
  
          ///
          System.out.println("GET - DIRECT:");
          start = System.currentTimeMillis();
          for (int i = 0; i < loops; i++) {
              int name = (int) p.getName();
          }
          end = System.currentTimeMillis();
          System.out.println("Runtime=" + ((end - start) / 1000.0) + "seconds");
  
          ////
          System.out.println("GET - LAMBDA:");
          start = System.currentTimeMillis();
          for (int i = 0; i < loops; i++) {
              int name = (int) lam.executeGetter(p);
          }
          end = System.currentTimeMillis();
          System.out.println("Runtime=" + ((end - start) / 1000.0) + "seconds");
  
          ///
          System.out.println("SET - REFLECTION:");
          int name = 12;
  
          start = System.currentTimeMillis();
          for (int i = 0; i < loops; i++) {
              field.set(p, name);
          }
          end = System.currentTimeMillis();
          System.out.println("Runtime=" + ((end - start) / 1000.0) + "seconds");
  
          ///
          System.out.println("SET - DIRECT:");
          name = 33;
          start = System.currentTimeMillis();
          for (int i = 0; i < loops; i++) {
              p.setName(name);
          }
          end = System.currentTimeMillis();
          System.out.println("Runtime=" + ((end - start) / 1000.0) + "seconds");
  
          ////
          System.out.println("SET - LAMBDA:");
  
          Double name2 = 2.3;
  
          start = System.currentTimeMillis();
          for (int i = 0; i < loops; i++) {
              lam.executeSetter(p, name2);
          }
          end = System.currentTimeMillis();
          System.out.println("Runtime=" + ((end - start) / 1000.0) + "seconds");
      }
  
  }
  

  ---

  package lambda;
  
  public class Person {
  
      public int name;
      private double salary;
  
      public int getName() {
          return name;
      }
  
      public void setName(int name) {
          this.name = name;
      }
  
      public double getSalary() {
          return salary;
      }
  
      public void setSalary(double salary) {
          this.salary = salary;
      }
  
  }
  
• Add non-lamda function to self of Python class

  Adding lambda expression to self of a Python class is easy:

  class Foo(object):
      def __init__(self, x):
          if x > 0:
              self.eval = lambda x: x
          else:
              self.eval = lambda x: x**2
  
          return
  
      def compute(self, y):
          return self.eval(y)
  

  In my case, self.eval is somewhat more complex such that it doesn't fit into a one-line lambda. I need def. How can I assign self.eval with a defined function though?

  For performance reasons, I would like to not store self.x = x and not move the if into compute.
• define a lambda function in single line using semicolons in python 3

  In python3, following works:

  print(3); print(5)
  

  However following gives a syntax error due to semicolon:

  (lambda key: (print(3); print(5)))
  

  Why is that, and is there a way to write a lambda function in single line (I intend to pass it as a short argument, without defining the function elsewhere)
• Error compiling in IntelliJ IDEA: "No MessageCollector"

  Edit: Solved. See @acdsee comment to see how.

  Since when I updated IntelliJ IDEA from 2017.3.5 to 2018.1, every project I start throws this error:

  Error:Module 'JBA' production: java.lang.Exception: LOGGING: Loading modules: [java.se, javafx.base, javafx.controls, javafx.fxml, javafx.graphics, javafx.media, javafx.swing, javafx.web, jdk.accessibility, jdk.attach, jdk.compiler, jdk.dynalink, jdk.httpserver, jdk.incubator.httpclient, jdk.jartool, jdk.javadoc, jdk.jconsole, jdk.jdi, jdk.jfr, jdk.jshell, jdk.jsobject, jdk.management, jdk.management.cmm, jdk.management.jfr, jdk.management.resource, jdk.net, jdk.packager, jdk.packager.services, jdk.scripting.nashorn, jdk.sctp, jdk.security.auth, jdk.security.jgss, jdk.unsupported, jdk.xml.dom, oracle.desktop, oracle.net, java.base, java.compiler, java.datatransfer, java.desktop, java.xml, java.instrument, java.logging, java.management, java.management.rmi, java.rmi, java.naming, java.prefs, java.scripting, java.security.jgss, java.security.sasl, java.sql, java.sql.rowset, java.xml.crypto, jdk.internal.jvmstat, jdk.management.agent, jdk.jdwp.agent, jdk.internal.ed, jdk.internal.le, jdk.internal.opt, jdk.jlink] (no MessageCollector configured)
• Theano error: no matching function for call to ‘batch_gemm<float>

  I'm trying to launch some Python projects which I need for my bachelor thesis and they use theano.

  The problem is, that one of the cell compiles these functions and fails with following compiler error: https://pastebin.com/TunvSwWU

  That's the piece of code which causes that:

  params_to_optimize  = [W_mean,U_mean,b_mean,softmax_W_mean,softmax_b_mean,h0_mean, var_log_sigma]
  train_fn = theano.function([X_tensor1, X_tensor2, Mask_matrix1, Mask_matrix2,  Y_vector], cost, updates=lasagne_adagrad(cost, params_to_optimize, learning_rate=lr), on_unused_input='ignore' )
  predict_fn = theano.function([X_tensor1, X_tensor2, Mask_matrix1, Mask_matrix2], output, on_unused_input='ignore')
  

  The strangest thing is that in other notebook I have this code and it compiles just fine:

  train_fn = theano.function([X_tensor1, X_tensor2, Mask_matrix1, Mask_matrix2,  Y_vector], cost, updates=lasagne_adagrad(cost, [W,U,h0,b,softmax_W,softmax_b], learning_rate=lr), on_unused_input='ignore' )
  predict_fn = theano.function([X_tensor1, X_tensor2, Mask_matrix1, Mask_matrix2], output, on_unused_input='ignore')
  

  I'm not really experienced theano user and right now just try to run this code before digging into it. What can be the problem?

  Update: It may have some problems with cost function which is this in compile-error case:

  softmax_cost = -T.sum(T.log(output)[T.arange(Y_vector.shape[0]), Y_vector])*X_train1.shape[0]/X_tensor1.shape[0]
  all_param_mean = [W_mean.flatten(),U_mean.flatten(), h0_mean.flatten(), b_mean.flatten(),softmax_W_mean.flatten(),softmax_b_mean.flatten()]
  all_param_tensor = T.concatenate(all_param_mean)
  first_part = T.exp(2*var_log_sigma)/T.exp(2*prior_log_sigma)
  second_part = T.dot(prior_mu- all_param_tensor,(prior_mu-all_param_tensor).T)/T.exp(2*prior_log_sigma)
  third_part = -np.sum([len(i.eval()) for i in all_param_mean])
  fourth_part = 2*prior_log_sigma - 2*var_log_sigma 
  KLD = 0.5* (first_part + second_part + third_part + fourth_part)
  cost = softmax_cost + KLD
  

  And this in compiling case:

  softmax_cost = -T.mean(T.log(output)[T.arange(Y_vector.shape[0]), Y_vector])
  all_params = T.concatenate([W.flatten(), U.flatten(), b, h0, softmax_W.flatten(), softmax_b])
  l2_cost = lambda2*(all_params**2).sum()
  cost = softmax_cost + l2_cost
  
• How to I remove csslint validation as a requirement to publish websites in visual studio?

  I ran into a stupid issue in visual studio this morning. I added in some css variables to a style sheet and tried to publish the site:

  :root
  {
  --main-color: #0059b3;
  --secondary-color: #99ccff;
  --highlight-color: #6600cc;
  --background-color: #000000;
  --window-color: #ffffff;
  --input-color: #eeeeee;
  }
  

  It runs fine locally, and renders w/o a problem in browsers. There are no build errors when i run a normal build. However, when I try to publish, I get a bunch of csslint errors, indicating the error is empty. I followed the link to provided, and it leads to a csslint github project, and after doing some reading, I found out that this is just a bug in csslint that isn't recognizing that this is a documented and legal feature of css.

  I hunted around in VS to try to cripple csslint, and while there is a switch in the tools/options menu to turn off csslint under the the css node, it doesn't appear to have any effect on the steps publish follows.

  I don't see anywhere that you can disable csslint on publish. Anyone know how I can cripple csslint until it is fixed?