equals-operator

问题 I have this code: ... #include "boost/tuple/tuple_comparison.hpp" ... template <typename ReturnType, typename... Args> function<ReturnType(Args...)> memoize(const Args && ... args) { using noRef = boost::tuple<typename std::remove_reference<Args>::type...>; static map<noRef, ReturnType, less<>> cache; auto key = std::tie(noRef{ boost::make_tuple(args ...) }); auto it = cache.lower_bound(key); ReturnType result; if (it->first == key) { ... But when I try to compile it I receive this error:

问题 I have some issues with the eval function. I have a list like, for example, list1 = [('a',1), ('b',2), ('c',3)] and I would like to assign each value of a tuple to the first element: for el in list1 : eval(el[0]) = el[1] How can I do this? 回答1: You could do this: exec('%s = %s' % el) But don't. Really, don't. You don't need dynamic local variables, you need a dictionary: my_dict = dict(list1) 回答2: You don't need eval for that. You can access local environment directly by calling the vars

问题 Error: error C2678: binary '==' : no operator found which takes a left-hand operand of type 'const entry' (or there is no acceptable conversion) The function: template <class T, int maxSize> int indexList<T, maxSize>::search(const T& target) const { for (int i = 0; i < maxSize; i++) if (elements[i] == target) //ERROR??? return i; // target found at position i // target not found return -1; } indexList.h indexList.cpp Is this suppose to be an overloaded operator? Being a template class I am

问题 I am trying to make a boolean test so that if one of the tire pressures is below 35 or over 45 the system outputs "bad inflation". In my class I must use a boolean, which is what I tried. However the boolean returned is always true. I don't understand why. public class tirePressure { private static double getDoubleSystem1 () //Private routine to simply read a double in from the command line { String myInput1 = null; //Store the string that is read form the command line double numInput1 = 0; /

问题 I have a vector of values, call it X, and a data frame, call it dat.fram. I want to run something like "grep" or "which" to find all the indices of dat.fram[,3] which match each of the elements of X. This is the very inefficient for loop I have below. Notice that there are many observations in X and each member of "match.ind" can have zero or more matches. Also, dat.fram has over 1 million observations. Is there any way to use a vector function in R to make this process more efficient?

问题 Can someone please put me out of my misery with this? I'm trying to figure out why a derived operator== never gets called in a loop. To simplify the example, here's my Base and Derived class: class Base { // ... snipped bool operator==( const Base& other ) const { return name_ == other.name_; } }; class Derived : public Base { // ... snipped bool operator==( const Derived& other ) const { return ( static_cast<const Base&>( *this ) == static_cast<const Base&>( other ) ? age_ == other.age_ :

问题 Can someone please put me out of my misery with this? I'm trying to figure out why a derived operator== never gets called in a loop. To simplify the example, here's my Base and Derived class: class Base { // ... snipped bool operator==( const Base& other ) const { return name_ == other.name_; } }; class Derived : public Base { // ... snipped bool operator==( const Derived& other ) const { return ( static_cast<const Base&>( *this ) == static_cast<const Base&>( other ) ? age_ == other.age_ :

问题 I got hit by a strange "asymmetry" in C# that I do not really understand. See the following code: using System; using System.Diagnostics; namespace EqualsExperiment { class Program { static void Main(string[] args) { object apple = "apple"; object orange = string.Format("{0}{1}", "ap", "ple"); Console.WriteLine("1"); Debug.Assert(apple.Equals(orange)); Console.WriteLine("2"); Debug.Assert(apple == orange); Console.WriteLine("3"); } } } It might be obvious for all you .NET gurus, but the 2nd

问题 With code like the following public class Task { string Name; public static bool operator ==(Task t1, Task t2) { return t1.Name = t2.Name && t1.GetType() == t2.GetType(); } } public class TaskA : Task { int aThing; public static bool operator ==(TaskA t1, TaskA t2) { return (Task)t1 == (Task)t2 && t1.GetType() == t2.GetType() && t1.aThing == t2.aThing; } } public class TaskB : Task //more of the same class Stuffin { List<Task> Tasks; void CheckIt() { bool theSame = Tasks[0] == Tasks[1]; } I'm

问题 I currently have a generic method where I want to do some validation on the parameters before working on them. Specifically, if the instance of the type parameter T is a reference type, I want to check to see if it's null and throw an ArgumentNullException if it's null. Something along the lines of: // This can be a method on a generic class, it does not matter. public void DoSomething<T>(T instance) { if (instance == null) throw new ArgumentNullException("instance"); Note, I do not wish to