Passing object reference to a method [duplicate]

ぐ巨炮叔叔 提交于 2019-12-11 03:28:37
问题 This question already has answers here : Is Java “pass-by-reference” or “pass-by-value”? (86 answers) Closed 5 years ago . If the Employee reference is made null in the changedetails(), variable id value is retained and NullPointerException is not thrown (Code 1) may be because we just pass a copy of object's reference, but in Code 2 why the variables value has changed Code 1: public class JavaPassing { public static void changedetails(Employee e) { e=null; } public static void main(String

Why does this empty dict break shared references?

风格不统一 提交于 2019-12-11 03:23:29
问题 I have found some Python behavior that confuses me. >>> A = {1:1} >>> B = A >>> A[2] = 2 >>> A {1: 1, 2: 2} >>> B {1: 1, 2: 2} So far, everything is behaving as expected. A and B both reference the same, mutable, dictionary and altering one alters the other. >>> A = {} >>> A {} # As expected >>> B {1: 1, 2: 2} # Why is this not an empty dict? Why do A and B no longer reference the same object? I have seen this question: Python empty dict not being passed by reference? and it verifies this

Trying to create copy function in a vector class

╄→尐↘猪︶ㄣ 提交于 2019-12-11 02:45:30
问题 I am working on implementing a vector class but cannot figure out how to write a function to copy one vector into another. template <class T> class Vec { public: //TYPEDEFS typedef T* iterator; typedef const T* const_iterator; typedef unsigned int size_type; //CONSTRUCTOS, ASSIGNMENT OPERATOR, & DESTRUCTOR Vec() {this->create(); } Vec(size_type n, const T& t = T()) { this->create(n, t); } Vec(const Vec& v) { copy(v); } Vec& operator=(const Vec& v); ~Vec() { delete [] m_data; } //MEMBER

Why this Ruby method passes it's argument by reference

落爺英雄遲暮 提交于 2019-12-11 02:21:20
问题 I answered on this question and stumbled on something strange. Ruby passes its arguments by value, the variables itself are references though. So why the first methods seems to pass its parameter by reference ? require 'set' require 'benchmark' def add_item1!(item, list) list << item unless list.include?(item) end def add_item2(item, list) list |= [item] end def add_item3(item, list) set = set << item list = set.to_a end array1 = [3,2,1,4] add_item1!(5, array1) p array1 # [3, 2,

Passing a reference by reference

不问归期 提交于 2019-12-11 01:56:56
问题 How could it be any useful to pass a reference object by reference. The regular usage is as the following: public static void main() { Student st = new Student(); st.FirstName = "Marc"; PutLastName(st); Console.WriteLLine(st.FirstName + " " + st.LastName); } public static PutLastName(Student student) { student.LastName = "Anthony"; } Why would anybody write the following, which does the same thing and does print: "Marc Anthony": public static void main() { Student st = new Student(); st

C passing variable by reference [closed]

雨燕双飞 提交于 2019-12-11 01:06:21
问题 This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. Closed 7 years ago . I have the following code: main() { uint8_t readCount; readCount=0; countinfunc(&readCount); } countinfunc(uint8_t *readCount) { uint8_t i; i = readCount

PHP architecture, and pass-by-reference vs pass-by-value

怎甘沉沦 提交于 2019-12-11 00:39:08
问题 Seeking suggestions from PHP architects! I'm not terribly familiar with PHP but have taken over maintenance of a large analytics package written in the language. The architecture is designed to read reported data into large key/value arrays, which are passed through various parsing modules to extract those report parameters known to each of those modules. Known parameters are removed from the master array, and any leftovers which were not recognized by any of the modules, are dumped into a

F#: How do I declare and use ByRef semantics on parameters?

时间秒杀一切 提交于 2019-12-10 22:28:24
问题 I am wraping some SQL Stored Procs with in/out parameters. This of course means I have to do ugly stuff like declare my parameters as by reference and use mutables. How would I do this in F#? 回答1: F# does indeed have a byref parameter. Here's an example from the MSDN page: type Incrementor(z) = member this.Increment(i : int byref) = i <- i + z Mutable variables also exist (though there's an important difference between using ref and mutable variables, either of which can be used for many of

Assign by reference PHP misunderstaning

纵饮孤独 提交于 2019-12-10 20:22:59
问题 Whats the meaning of $arr[0] result "2" in the code given below, $arr2 is copying $arr and increasing its first value by one, so the result of $arr2[0] "2" is understaning,but whats happening with $arr, when i pass by reference $arr[0] to $a like so $a=&$arr[0] the result of $arr[0] is 2, when i pass it by value $a=$arr[0[ the result of $arr[0] would be set to 1 as it should, can anyone enlighten me on this? <?php $a = 1; $arr = array(1); $a = &$arr[0]; $arr2 = $arr; $arr2[0]++; echo $arr[0].

c++ copy construct parameter passed by value

你说的曾经没有我的故事 提交于 2019-12-10 18:48:52
问题 I want freeFunct to do non const stuff on its own copy of object a. Let's say that freeFunct is required to be a free function because in real code cases it takes many different parameters, calls several public functions from all of them and there is no point in making it a non-static member function of any class. Three different ways of declaring it come to my mind. I have the feeling that the third solution is the worse. Is there any difference between the first two? Is there something