variable-assignment

问题 Javascript allows swapping of variables: var x = 1 var y = 2 [x, y] = [y, x] // y = 1 , x = 2 And destructured assignment: var a, b [a, b] = [1, 2] log(a) // 1 log(b) // 2 When using variable swapping in lieu with destructured assignment, trying to swap variables breaks down: var a, b [a, b] = [1, 2] // a = 1, b = 2 [a, b] = [b, a] // TypeError: Cannot set property '2' of undefined Why is that? 回答1: If you decide to omit semicolons (no judgement, I prefer it that way too), don't forget to

问题 For example I have this set k=5 of elements [1,2,3,4,5] and I want all permutations of length n=2 . 1,2 1,3 1,4 1,5 2,1 etc etc. Thing is i can't use STL, external math libraries etc. I've been sitting on this problem for about 3 days now and im about to go crazy. What i tried is generating all permutations of all the elements using Heap's algorithm, and then all the permutations of n elements where contained in the first n numbers of all k-permutations and i could just truncate and delete

问题 I'm creating variables based on certain string combinations. Each variable would store some values. In this example, to make it simple, they store a numerical value. However, in actual problem, each would store a tibble . I need to store each tibble as RData and they have to be created using unique combinations of the string. The problem is when I use save() on this variable, it couldn't find it so the save would fail. res <- 12345 sku = 'sku_a' index = '1' # create variable based on string

问题 I'm currently trying to split an array of chars that is assigned from reading in from a text file. right now I'm having troubles with delimiters and I don't know if I can have multiple. what I want to delimit is commas and spaces. Here is my code so far. #include <stdio.h> FILE * fPointer; fPointer = fopen("file name", "r"); char singleLine[1500]; char delimit[] = int i = 0; int j = 0; int k = 0; while(!feof(fPointer)){ //the i counter is for the first line in the text file which I want to

问题 Consider the following two assignments. $ a="foo bar" $ b=$a $ b=foo bar bash: bar: command not found Why does the second assignment work fine? How is the second command any different from the third command? I was hoping the second assignment to fail because b=$a would expand to b=foo bar Since $a is not within double-quotes, foo bar is not quoted, therefore field-splitting should occur (as per my understanding) which would result in b=foo to be considered an assignment and bar to be a

问题 I have two questions related to DateTime assingments DateTime? y = 1 == 1 ? null: DateTime.MaxValue; DateTime? y = null; // assignment works as expected Why the first assignment issues error of type conversion between null and DateTime? Which is the preferred way for null assignments of DateTime? in c#. DateTime? x = default(DateTime?); //prints null on console DateTime? x = null; // prints null on console DateTime? x = DateTime.MinValue; //print 01/01/0001 回答1: The second statement DateTime?

问题 I'm trying to conduct a certain a calculation using purrr::map2() taking two different arguments. purrr::map2( .x = c(1, 3), .y = c(10, 20), function(.x, .y)rnorm(1, .x, .y) ) purrr::map2() returns a list, but I want to assign a distinct object name to each content within the list. For example, I want to name the first list [[1]] [1] -5.962716 as model1 and [[2]] [1] -29.58825 as model2 . In other words, I'd like to automate the object naming like model* <- purrr::map2[[*]] . Would anybody

问题 As it pertains to Delphi... When a variable is declare of a certain type, is it initialized to an OBJECT of that type? Or must the variable be assigned an expression which returns an object of that type? I'm coming from a strong Java background. What I mean to ask is this... In Java, say you declare an instance variable of a user defined type named Orange. Which would look like this: private Orange _fruit; The variable _fruit still holds a reference to null until actually assigned an instance

问题 I want to forbid further assignments on some attributes of a class after it was initialized. For instance; no one can explicitly assign any value to 'ssn' (social security number) property after the Person instance 'p' has been initialized. _ setattr _ is also being called while assigning the value inside _ init _ method, thus it is not what I want. I'd like to restrict only further assignments. How can I achieve that? class Person(object): def __init__(self, name, ssn): self.name = name self

问题 My question is from a popular coding test. Given a chain defined as follows: class ListNode: def __init__(self, x): self.val = x self.next = None If we want to revert the chain, for example: Input:1->2->3->4->5->NULL Output: 5->4->3->2->1->NULL It can be solved like this: class Solution: def reverseList(self, head: ListNode) -> ListNode: cur, pre = head, None while cur: tmp = cur.next cur.next = pre pre = cur cur = tmp return pre But there is a more compact way, which I can't really follow: