casting

问题 In Java, I can write code like: void cast(A a) { if(a instanceof Person) { Person p = (Person) a; } } In Kotlin, what should I do? Use as operator or is operator? 回答1: is X is the equivalent of instanceof X foo as X is the equivalent of ((X) foo) Additionally, Kotlin performs smart casting where possible, so no additional cast needed after you check the type using is : open class Person : A() { val foo: Int = 42 } open class A and then: if (p is Person) { println(p.foo) // look, no cast

问题 In Java, I can write code like: void cast(A a) { if(a instanceof Person) { Person p = (Person) a; } } In Kotlin, what should I do? Use as operator or is operator? 回答1: is X is the equivalent of instanceof X foo as X is the equivalent of ((X) foo) Additionally, Kotlin performs smart casting where possible, so no additional cast needed after you check the type using is : open class Person : A() { val foo: Int = 42 } open class A and then: if (p is Person) { println(p.foo) // look, no cast

问题 I have seen in Java code in many places, people tend to cast between primitives int and char. Is this necessary? Are they not implicitly converted. For e.g. I tried this and exactly got what I should. Then why do people explicitly cast? Am I missing something? char a = 'a'; int index = (int) a; index = 98; a = 98; System.out.println(index); System.out.println(a); 回答1: Sometimes people will cast for clarity, sometimes for overloading reasons, and sometimes for reasons of ignorance. For example

问题 What am I doing? I want to make mapping of an object field-by-field to objects of some generic type. I have 4 runtime cases (with runtime check and throwing exception if not matches) that I've used as a properties of original object: false transforms to Smth<unknown> | undefined true transforms to Smth<unknown> [] transforms to Smth<unknown> with 0 or more elements [true] transforms to Smth<unknown> with 1 or more elements Actually that's not very difficult, but I'm not very happy to have

问题 This question already has answers here : How to call a parent method from child class in javascript? (8 answers) Closed 10 days ago . class Parent { constructor(x) { this.x = x; } present() { return `I have a ${this.x}`; } } class Child extends Parent { constructor(x, y) { super(x); this.y = y; } present() { return `${super.present()}, it is a ${this.y}`; } } child = new Child("Tinggu", "Winggu"); console.log(child.present()); // invokes the child version How would I invoke the parent's

问题 This question already has answers here : How to call a parent method from child class in javascript? (8 answers) Closed 10 days ago . class Parent { constructor(x) { this.x = x; } present() { return `I have a ${this.x}`; } } class Child extends Parent { constructor(x, y) { super(x); this.y = y; } present() { return `${super.present()}, it is a ${this.y}`; } } child = new Child("Tinggu", "Winggu"); console.log(child.present()); // invokes the child version How would I invoke the parent's

问题 host.cpp has: int main (void) { void * th = dlopen("./p1.so", RTLD_LAZY); void * fu = dlsym(th, "fu"); ((void(*)(int, const char*)) fu)(2, "rofl"); return 0; } And p1.cpp has: #include <iostream> extern "C" bool fu (float * lol) { std::cout << "fuuuuuuuu!!!\n"; return true; } (I intentionally left errors checks out) When executing host, “fuuuuuuuu!!!” is printed correctly, even though I typecasted the void pointer to the symbol with a completely different function signature. Why did this

问题 Requirement : One particular column in a DataFrame is 'Mixed' Type. It can have values like "123456" or "ABC12345" . This dataframe is being written into an Excel using xlsxwriter . For values like "123456" , down the line Pandas converting it into 123456.0 ( Making it look like a float) We need to put it into xlsx as 123456 (i.e as +integer) in case value is FULLY numeric. Effort : Code Snippet shown below import pandas as pd import numpy as np import xlsxwriter import os import datetime

问题 This question already has answers here : How do I convert a Vec<T> to a Vec<U> without copying the vector? (2 answers) Closed 7 months ago . Is there a better way to cast Vec<i8> to Vec<u8> in Rust except for these two? creating a copy by mapping and casting every entry using std::transmute The (1) is slow, the (2) is "transmute should be the absolute last resort" according to the docs. A bit of background maybe: I'm getting a Vec<i8> from the unsafe gl::GetShaderInfoLog() call and want to

问题 I'm newbie in Rust from Python. I believe it's a basic question, but I am too new to find the answer by keywords like Type Casting Option . In Python, to make the type checker know return type is not Optional[int] + int , we can address assert logic to enforce the type checker know x will never be None after line assert . from typing import Optional def add_one(x: Optional[int] = None) -> int: if x is None: x = 0 assert x is not None return x + 1 if __name__ == '__main__': add_one(0) # 1 add