17,337 questions
3
votes
1
answer
208
views
Use decltype(auto) return type to sometimes return references
I have the following code to normalize std::filesystem::path to always use forward slashes as separators:
static decltype(auto) fix_path_separator(const std::filesystem::path& path) {
if ...
- 3,144
1
vote
1
answer
100
views
Use a reference to $a to make $a a reference to $b
I have an array $arr = ['a', ['b',['c','d','e']]];.
So $arr[1][1][0] is 'c'.
I have these indexes listed in n array: $idx = [1,1,0];
(this may sound tricky, but comes from the fact that I got them ...
- 818
0
votes
1
answer
75
views
How to assign a new object to a reference?
Why can't I do it like this in Go?
func do(m1 map[int]string) {
var m map[int]string = make(map[int]string)
*m1 = &m;
}
I have m1 map, which means I can now it's reference? How to assign ...
- 1,988
1
vote
1
answer
113
views
Avoiding double references in Rust
I have the following utility method to get raw bytes of an object (to send via network, etc.):
pub fn to_bytes<T>(data: &T) -> &[u8] {
unsafe { slice::from_raw_parts((data as *...
- 641
5
votes
1
answer
178
views
Segmentation fault when trying to assign a global variable to a static reference variable
The following program gives segmentation fault.
#include <iostream>
using namespace std;
class A {
public:
static int& a;
};
int a = 42;
int& A::a = a;
int main() {
a = 100;
...
- 749
0
votes
0
answers
117
views
Making sense of const rvalue reference [duplicate]
I'm trying to understand the rvalue references in C++. Here's what I think they represent.
Say we have an object, O. This object exists on the stack and has the name O. This makes this object a lvalue....
- 1,086
0
votes
0
answers
60
views
The mutable reference I return from a function in Rust seems to violate the borrowing rules — how is this possible? [duplicate]
I have a mutable variable and a mutable reference to it. When I pass this reference to a function and return it back from there, it seems to violate Rust’s borrowing rules. What’s the reason for this?
...
- 9
2
votes
1
answer
162
views
c++20 tuple compare with reference
We upgrade our codebase from c++17 to c++20 lately, and some code does not work as before. I take the following simplified sample code as show case here.
None of the overloaded compare operators is ...
- 343
1
vote
2
answers
112
views
Creating virtual object in constructor initialization
I want to create a variable of type Foo. The class Foo consists of a variable called Bar bar_ which is filled directly in the constructor initialization. The thing is, class Bar has a reference to the ...
- 59
1
vote
1
answer
89
views
Simplifying getting a specific type from an enum
I have a set of classes linked into an enum:
#[derive(Default)]
pub struct A {
}
#[derive(Default)]
pub struct B {
}
#[derive(Default)]
pub struct C {
}
enum Classes {
A(A),
B(B),
C(C),
...
- 38k
5
votes
2
answers
309
views
Can an rvalue of a specific class type be automatically cast to an lvalue of itself?
In C++, a function with signature void f(A& a) (non-template) only binds to a lvalue.
Is it possible for an rvalue to automatically cast itself to an lvalue?
This is what I tried:
#include <...
- 16.7k
12
votes
1
answer
295
views
C++ temporary objects and constant reference
I am going through "C++ Primer", and it is mentioned that for the following code:
double dval = 3.14;
const int &ri = dval; //Bind a const int to a plain double object.
The ...
- 121
0
votes
1
answer
80
views
How to reference a second Pandas dataframe to the first one without creating any copy of the first one?
I have a large pandas dataframe df of something like a million rows and 100 columns, and I have to create a second dataframe df_n, same size as the first one. Several rows and columns of df_n will be ...
- 165
28
votes
1
answer
2k
views
Why is `&self` allowed in the parameters of `&mut self` methods, but not `&mut self`?
Rust method calls are desugared to fully-qualified-syntax and function parameters are evaluated left to right. Why then does s.by_mut(s.by_ref(())) compile while other
expressions don't?
struct S;
...
- 537
0
votes
2
answers
86
views
How can the italicized text be referenced in other cells?
I asked a question about italicizing specific parts of a cell (Making variable strings of text italics in Excel VBA).
I run the macro in column N to get what I want italicized, but when I reference ...
- 51