C++ function with a generic and optional class

C++ function with a generic and optional class

By : user2185837
Date : November 23 2020, 04:01 AM
will be helpful for those in need template argument deduction don't perform implicit conversions.
The issue here is that you passing a pointer to function to fun which is double (*) (std::vector, c_myclass) and the function parameter is expecting std::function, OptionalClass)>, and is using a template parameter that at that moment is unknown.
code :
galg(std::function(f), par, extra)
template <class T> struct identity {using type = T;};
template <class T> using identity_t = typename identity<T>::type;

template <class OptionalClass>
double galg(identity_t<std::function<double(std::vector<double>,OptionalClass)>> func, std::vector<double>& params, OptionalClass extra);

galg(fun, par, extra);

Share : facebook icon twitter icon
Can I make a generic optional, defaulting to a certain class?

Can I make a generic optional, defaulting to a certain class?

By : krishna
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , I don't think there's much you can do about it, to be honest. You could make Foo doubly generic:
code :
public class Foo<TData, TArgs> where TArgs : FooEventArgs<TData>
    public delegate void EventHandler<TArgs>(object sender, TArgs e);
    public event EventHandler<TArgs> Changed;
public class Foo : Foo<object, FooEventArgs>
public interface IFoo
    // Members which don't depend on the type parameter

public interface IFoo<T> : IFoo
    // Members which all use T
return optional from generic function in c++

return optional from generic function in c++

By : Mace
Date : March 29 2020, 07:55 AM
seems to work fine First of all, boost::optional or std::optional were made exactly for that case. Is there a reason why you don't want to use them? Because most solutions will either mimic std::optional or they are a poor replacement.
Pass an output parameter by reference.
code :
template <class T>
bool search( T arg, T & out );
template <class T>
const T & search( T arg );
template <class T>
const T * search( T arg );
template <class T>
struct DummyValue;

template <>
struct DummyValue<int>
    static constexpr const int value = -1;
    // Or:
    // static int makeDummyValue();
// And so on ...
How to declare optional class property with generic `Results`

How to declare optional class property with generic `Results`

By : Joshua Holloway
Date : March 29 2020, 07:55 AM
help you fix your problem Unfortunately, you will probably have to turn Results into [Car] in order for this to work. The built-in Swift collections are covariant, but any user-defined Swift generic type (including user-defined collections) is invariant. There's no way right now to specify otherwise.
iOS 12 SDK Generic function returns Optional.some(nil)

iOS 12 SDK Generic function returns Optional.some(nil)

By : saeba lee
Date : March 29 2020, 07:55 AM
may help you . This is due to an intentional change (#13910) where the compiler is now more conservative with unwrapping an optional value that's being cast to a generic placeholder type. Now, the results you get are more consistent with those that you would get in a non-generic context (see SR-8704 for further discussion).
For example:
code :
// note the constraint `where Key : ExpressibleByStringLiteral` is needlessly restrictive.
extension Dictionary where Key : ExpressibleByStringLiteral {
  func find<T>(key: Key) -> T? {
    return self[key] as? T

let dict: [String: Any] = ["foo": "bar"]

let genericBar: Any? = dict.find(key: "bar")
print(genericBar as Any) // in Swift 4.1: nil, in Swift 4.2: Optional(nil)

// `T` in the above example is inferred to be `Any`.
// Let's therefore substitute `as? T` with `as? Any`.
let nonGenericBar = dict["bar"] as? Any
print(nonGenericBar as Any) // in both versions: Optional(nil)
extension Dictionary {
  func find<T>(key: Key) -> T? {
    return (self[key] as? T?) ?? nil
extension Dictionary {
  func find<T>(key: Key) -> T? {
    guard let value = self[key] else { return nil }
    return value as? T
extension Dictionary {
  func find<T>(key: Key) -> T? {
    return self[key].flatMap { $0 as? T }
Compilation error with Optional in generic class

Compilation error with Optional in generic class

By : Tharaa Browner
Date : March 29 2020, 07:55 AM
may help you . I have an unexplained compilation error with guava Optional I have this test for demonstrate : , In the line
Related Posts Related Posts :
  • C++ on Vistual Studio with CMake error: manifest 'build.ninja' still dirty after 100 tries
  • Is there a way to automatically resolve an overloaded method via a template parameter?
  • Fastest way to find pair in a vector, remove it while iterating
  • error C2440: '=': cannot convert from 'const char *' to 'LPCWSTR'
  • Unable to call boost::clear_vertex while using listS for the vertex and edge lists
  • Decoding binary data from serial port
  • Pattern to Implement an OO interface to a C program written in an imperative style
  • CEPH + Librados++ is not returning consisten results
  • `LoadLibraryExW` triggers exception `0xC0000023` from `NtMapViewOfSection`
  • static_cast to a struct type to access all of its member variable
  • Forward declaration for boost::intrusive_ptr class to reduce compile time
  • How to use priority_queue with a non-static compare method of class instance?
  • Template parameters inside and outside class/struct
  • Determining prime number
  • How to resolve ambiguity between constructors taking std::string and std::vector
  • My program crashes when I try to change private values from an object
  • Unordered_map with custom class as key
  • Strict aliasing rules broken with templates and inheritance
  • C++ Derived Class Override Return Type
  • singly linked list c++ constructor, destructor and printing out
  • How to clone class with vector of unique_ptr to base class
  • error: no match for operator
  • std::vector doesnt accept my struct as template
  • selection of people's contours
  • how to fix the (Error using mexOpenCV) on matlab?
  • Is or was there a proposal for c++ to use the context for short enum values?
  • Fair assumptions about std::hash implementations
  • undefined reference to libusb using cyusb
  • Function returns null pointer instead of address
  • C++17 copy elision and object destruction
  • Input multiple strings via operator>> c++
  • Avoiding overflow boost container
  • How to Write a Lambda Wrapping a Function with Optional Return Value
  • Partial specialization with more template parameters
  • How to convert fixed size array to pointer on pointer array
  • Memory leak in const member constructor with tag dispatching
  • Custom QGraphicsItem That Contains Child QGraphicsItems
  • Are There Restrictions on What can be Passed to auto Template Parameters?
  • Rotating line inside rectangle bounds
  • Why do I need dynamic memory allocation if I can just create an array?
  • How can I convert a text file into a form that MPI_Bcast can send?
  • How to get array of all `this` of an instance
  • Using pointers as parameters
  • Automatic type deduction with const_cast is not working
  • Why does std::is_rvalue_reference not do what it is advertised to do?
  • Function Template Specialization with Forward Declared Type
  • template deduction failed in vector
  • Is there a signed `sizeof` alternative in Qt
  • clarification on overloading the -> operator
  • What is __m128d?
  • QtConcurrent: why releaseThread and reserveThread cause deadlock?
  • Function receiving different value than passed
  • Can C++ close a '''fstream''' variable after '''.close()'''?
  • Is it necessary to overload operator in this specific case
  • Comparing an element of a string array with a string
  • how to dereference a pointer of a map of pointers to objects in c++
  • How recursive function control flow change for static variable?
  • SDL 2 blitting BMP File
  • Why does an extremely large value cause this code to repeat infinitely?
  • Function returning different value than what is in function body before return statement
  • shadow
    Privacy Policy - Terms - Contact Us © bighow.org