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Implementing a class of "constants" initialized at application start not at compile time


Implementing a class of "constants" initialized at application start not at compile time

By : user2953583
Date : November 21 2020, 01:01 AM
hope this fix your issue Well, using system properties is a way of doing it unless there is a huge amount of constants.
code :
private static final String CONSTANT1 = System.getProperty("my.system.property");
private static final int CONSTANT2 = Integer.valueOf(System.getProperty("my.system.property"));
public class Constants {
    private static final String CONSTANT1 = System.getProperty("my.system.property");
    private static final int CONSTANT2 = Integer.valueOf(System.getProperty("my.system.property"));
    private static final String CONSTANT3;
    private static final String CONSTANT4;

    static {
        try {
            final Properties props = new Properties();
            props.load(
                new FileInputStream(
                        System.getProperty("app.properties.url", "app.properties")));

            CONSTANT3 = props.getProperty("my.constant.3");
            CONSTANT4 = props.getProperty("my.constant.3");
        } catch (IOException e) {
            throw new IllegalStateException("Unable to initialize constants", e);
        }
    }
}


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Can we have a "not override a concrete method ..." compile time error when implementing interfaces?

Can we have a "not override a concrete method ..." compile time error when implementing interfaces?


By : Ricardo Wolosker
Date : March 29 2020, 07:55 AM
Any of those help Java ships with annotation processor capabilities, starting from Java 6: Source Code Analysis. (Technically it's part of Java 5, but Java 6 integrated it into the compiler phase rather than a special tool). Sun provides this Getting Started guide.
An annotation processor gets invoked by the compiler while building the project, and may issue errors just like the compiler does. It's a neat way to enforce more rules than Java specifies.
code :
@SupportedSourceVersion(SourceVersion.RELEASE_6)
@SupportedAnnotationTypes("*")
public class CheckMethodOverride extends AbstractProcessor {
    // returns true if the class has a method with the specified method name
    // and specified number of parameters
    private static boolean hasMethod(TypeElement clazz, String methodName, int arity) {
        for (ExecutableElement method : 
                 ElementFilter.methodsIn(clazz.getEnclosedElements())) {
            if (method.getSimpleName().equals(methodName)
                    && method.getParameters().size() == arity)
                return true;
        }
        return false;
    }

    // the interface whose subclasses must override hashCode and equals
    TypeMirror interfaceToCheck;

    @Override
    public void init(ProcessingEnvironment env) {
        interfaceToCheck = env.getElementUtils().getTypeElement("com.notnoop.myinterface").asType();
    }

    @Override
    public boolean process(Set<? extends TypeElement> annotations,
            RoundEnvironment roundEnvironment) {
        for (TypeElement e :
            ElementFilter.typesIn(roundEnvironment.getRootElements())) {
            if (this.processingEnv.getTypeUtils()
                     .isSubtype(e.asType(), interfaceToCheck)
                && (!hasMethod(e, "equals", 0)
                    || !hasMethod(e, "hashCode", 0))) {
                processingEnv.getMessager().printMessage(Kind.ERROR,
                    "Class " + e + " doesn't override hashCode or equals", e);
            }
        }
        return true;
    }
}
Compile time error "final variable is not initialized"

Compile time error "final variable is not initialized"


By : Replicant
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I have an issue, while trying few code snippets i came across a code
code :
final int i;
 O(int j)// error here as THE BLANK FINAL FIELD i IS NOT INITIALIZED
    {
        j=20;
        System.out.println(j);
    }
Gemfile constants redefinition, "warning: already initialized constant"

Gemfile constants redefinition, "warning: already initialized constant"


By : Bryn Edwards
Date : March 29 2020, 07:55 AM
Does that help I would start by forking engtagger Then remove the file with the constant that's already been initiated through the other gem, commit your changes to the newly created fork.
Add it to your Gemfile
code :
gem engtagger, github: 'your_github_handle/engtagger'
Implementing a compile-time "static-if" logic for different string types in a container

Implementing a compile-time "static-if" logic for different string types in a container


By : glucadb
Date : March 29 2020, 07:55 AM
it helps some times I'd like to write a function template that operates on a container of strings, for example a std::vector.
code :
#include <type_traits>

template <typename T, typename F>
auto static_if(std::true_type, T t, F f) { return t; }

template <typename T, typename F>
auto static_if(std::false_type, T t, F f) { return f; }

template <bool B, typename T, typename F>
auto static_if(T t, F f) { return static_if(std::integral_constant<bool, B>{}, t, f); }

template <bool B, typename T>
auto static_if(T t) { return static_if(std::integral_constant<bool, B>{}, t, [](auto&&...){}); }
template <typename ContainerOfStrings>
void DoSomething(const ContainerOfStrings& strings)
{
    for (const auto & s : strings)
    {
        static_if<std::is_same<typename ContainerOfStrings::value_type, CString>{}>
        ([&](auto& ss)
        {
            // Use the CString interface
            ss.GetLength();
        })(s);

        static_if<std::is_same<typename ContainerOfStrings::value_type, wstring>{}>
        ([&](auto& ss)
        {
            // Use the wstring interface
            ss.size();
        })(s);
    }
}
Can I detect at compile time "function arguments" that are compile-time constants

Can I detect at compile time "function arguments" that are compile-time constants


By : Matthew Yarlett
Date : March 29 2020, 07:55 AM
To fix the issue you can do
it doesn't have to be a plain function void print(int i) - it could be a function-like macro that does some magic on its arguments and calls a different function depending on whether it is a constant, or it could be some template magic
code :
template <typename T>
struct PrintStruct
 {
   template <bool>
   static void func (...) 
    { std::cout << "func non-const: " << T::func(true) << std::endl; }

   template <bool b, int I = T::func(b)>
   static void func (int) 
    { std::cout << "func const:     " << I << std::endl; }
 };
#define Print(i)                          \
[&]()                                     \
 {                                        \
   static int const printLocalVar { i };  \
                                          \
   struct local_foo                       \
    {                                     \
      static constexpr int func (bool b)  \
       { return b ? printLocalVar : 0; }  \
    } ;                                   \
                                          \
   PrintStruct<local_foo>::func<true>(0); \
 }                                        \
()
#include <iostream>

template <typename T>
struct PrintStruct
 {
   template <bool>
   static void func (...) 
    { std::cout << "func non-const: " << T::func(true) << std::endl; }

   template <bool b, int I = T::func(b)>
   static void func (int) 
    { std::cout << "func const:     " << I << std::endl; }
 };


#define Print(i)                          \
[&]()                                     \
 {                                        \
   static int const printLocalVar { i };  \
                                          \
   struct local_foo                       \
    {                                     \
      static constexpr int func (bool b)  \
       { return b ? printLocalVar : 0; }  \
    } ;                                   \
                                          \
   PrintStruct<local_foo>::func<true>(0); \
 }                                        \
()

int main()
 {
   constexpr int  i { 2 };
   int const      j { 3 };
   int            k { 4 };
   int const      l { k+1 };

   Print(1);    // print func const:     1
   Print(i);    // print func const:     2
   Print(j);    // print func const:     3
   Print(k);    // print func non-const: 4
   Print(l);    // print func non-const: 5
   Print(2+2);  // print func const:     4
 }
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