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F# record member evaluation

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问题 Why is t.b evaluated on every call? And is there any way how to make it evaluate only once? type test = { a: float } member x.b = printfn "oh no" x.a * 2. let t = { a = 1. } t.b t.b 回答1: It's a property; you're basically calling the get_b() member. If you want the effect to happen once with the constructor, you could use a class: type Test(a:float) = // constructor let b = // compute it once, store it in a field in the class printfn "oh no" a * 2. // properties member this.A = a member this.B

Delete vector class member

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问题 I have a class A with a member which is a vector of object pointers of another class B class A { std::vector<B*> m_member_A m_member_A is populated by creating objects of B by using new operator B* b1 = new B; m_member_A.push_back(b1); In A's destructor, is the following correct to free up everything? A::~A() { for(int i = 0; i < m_member_A.size(); ++i) { delete m_member_A[i]; } m_member_A.clear(); } 回答1: It's correct, as long as you also have a correct copy constructor and copy-assignment

getter and setter for class in class c#

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问题 Assuming we have a class InnerClass with attributes and getter/setter. We also have a class OuterClass containing the InnerClass. e.g. class InnerClass { private int m_a; private int m_b; public int M_A { get { return m_a; } set { m_a = value; } } } class OuterClass { private InnerClass innerClass } How would I implement a correct getter and setter for the innerClass member of OuterClass? Thanks in advance! 回答1: The syntax wouldn't be any different. Just... public InnerClass InnerClass { get

getter and setter for class in class c#

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Member Pointer to Base Class

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问题 all. I can't undestand why the bellow code need a cast to work. Someone can explain it? class Base { }; class Derived : public Base { }; class Class { public: Derived member; }; ... Derived obj; Base *ptrObj = &obj; // ok, no cast needed Derived Class::* ptr = &Class::member; // ok Base Class::* ptr = &Class::member; // wrong, need cast, why? 回答1: Because if Base were allowed (covariant), you could then do this, which is a no-no: Base Class::* ptr = &Class::member; Class obj; obj.*ptr = Base(

enable class's member depending on template

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问题 I already know that you can enable (or not) a class's method using std::enable_if for exemple: template<size_t D, size_t E> class Field { ... size_t offset(const std::array<float,D>& p) const { ... } template<typename TT = size_t> typename std::enable_if<D!=E, TT>::type offset(const std::array<float,E>& p) const { return offset(_projection(p)); } ... }; This helps not being able to call function that are invalid in a specific case as well as removing overloading errors ... which, to me, is

redis的有序集合ZSET(stored set)

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相关命令 1.ZADD 　　ZADD key-name score member [score member……] 　　将带有给定分值的成员添加到有序集合里 2.ZREM 　　ZREM key-name member [ member……] 　　从有序集合中删除指定的成员 php示例 $redis = new redis(); $redis->connect('127.0.0.1', 6609); $redis->delete('sc1'); $redis->delete('sc2'); $redis -> zAdd('sc1',1,'k1',2,'k2',3,'k3',4,'k4',5,'k5'); $redis -> zAdd('sc1',6,'k6'); $redis -> zAdd('sc1',7,'k7'); var_dump($redis->zRange('sc1', 0, -1)); echo "<br/>"; //结果 array(7) { [0]=> string(2) "k1" [1]=> string(2) "k2" [2]=> string(2) "k3" [3]=> string(2) "k4" [4]=> string(2) "k5" [5]=> string(2) "k6" [6]=> string(2) "k7" } //rem var_dump(

select an union member depending on a template parameter

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问题 I'm dealing with an union in C++, and I would like have a function template which access to the active union member depending on a template parameter. Code is something like (doSomething is just an example): union Union { int16_t i16; int32_t i32; }; enum class ActiveMember { I16 , I32 } template <ActiveMember M> void doSomething(Union a, const Union b) { selectMemeber(a, M) = selectMember(b, M); // this would be exactly (not equivalent) the same // that a.X = b.X depending on T. } To

C# Class Auto increment ID

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问题 I am creating a class in C# called "Robot", and each robot requires a unique ID property which gives themselves an identity. Is there any way of creating an auto incremental ID for each new class object? So, If i created 5 new robots, their IDs respectively will be 1, 2, 3, 4, 5. If I then destroy robot 2 and create a new robot later, it will have the ID of 2. And if I add a 6th it will have the ID of 6 and so on.. Thanks. 回答1: This will do the trick, and operate in a nice threadsafe way. Of

C++ member function as callback function to external library

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问题 So below is a basic idea of what I'm trying to do. I have an external library that I would like to use in an existing project. I cannot change anything in the external library or the main function in the existing project of course. The problem I face is how to pass a callback function I make in my class to this external function as a pointer to function. At the same time, this callback function has to have access to members of the class so I cannot simply make it static. How can I do it?