A mutable can be modified after it is created.
A mutable can be modified after it is created. It is a keyword in functional programming opposite to immutable.
Related tags:
Questions tagged [mutable]
1184 questions
11
votes
1 answer
What is the difference between matching a mutable Option reference in "if let Some(ref mut x) = option" and in "if let Some(x) = option.as_mut()"?
Background
Consider a toy problem in which I have a Node struct that represents nodes of linked lists and that I want to create a function that builds a list with values from 1 to 9. The following code works as expected:
struct Node {
val: i32,
…
luca_moller
- 156
- 7
11
votes
5 answers
How to solve ImportError: dlopen(): Symbol not found:.... Expected in: flat namespace
Can anyone help me solve this issue?
ImportError: dlopen(/Users/......./venv/lib/python3.6/site-packages/recordclass/mutabletuple.cpython-36m-darwin.so, 2): Symbol not found: __PyEval_GetBuiltinId
Referenced from:…
Oliver Robie
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11
votes
2 answers
How to convert immutable Seq to mutable seq with until loop
I'm trying to return a mutable Sequence with an until loop, but i have an immutable seq in return of (0 until nbGenomes) :
def generateRandomGenome(nbGenomes:Int): IndexedSeq[GenomeDouble]={
return ((0 until nbGenomes toSeq).map{e =>…
reyman64
- 523
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11
votes
1 answer
How to get functools.lru_cache to return new instances?
I use Python's lru_cache on a function which returns a mutable object, like so:
import functools
@functools.lru_cache()
def f():
x = [0, 1, 2] # Stand-in for some long computation
return x
If I call this function, mutate the result and…
jmd_dk
- 12,125
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11
votes
3 answers
How do I pass a mutable list to a bundle?
I want to add a mutable list to a bundle, but there doesn't seem to be a way to accomplish this.
var bundle = Bundle()
bundle.put...????("LIST", fbModel.recipeArray)
You can use putString and so on, but there doesn't seem to be a…
tore
- 619
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11
votes
4 answers
Is modifying a value type from within a using statement undefined behavior?
This one's really an offshoot of this question, but I think it deserves its own answer.
According to section 15.13 of the ECMA-334 (on the using statement, below referred to as resource-acquisition):
Local variables declared in a
…
Dan Tao
- 125,917
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- 447
11
votes
2 answers
How to mutate a list with a function in python?
Here's a pseudocode I've written describing my problem:-
func(s):
#returns a value of s
x = a list of strings
print func(x)
print x #these two should give the SAME output
When I print the value of x in the end, I want it to be the one returned…
Ritvik Sharma
- 113
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11
votes
1 answer
PickleType with Mutable Tracking in SqlAlchemy
I have a project where I would like to store a large structure (nested objects) in a relational db (Postgres). It's part of a larger structure and I don't really care about the serialization format - I'm happy for it to be a blob in a column - I'd…
Aidan Kane
- 3,856
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11
votes
5 answers
Generating sublists using multiplication ( * ) unexpected behavior
I'm sure this has been answered somewhere but I wasn't sure how to describe it.
Let's say I want to create a list containing 3 empty lists, like so:
lst = [[], [], []]
I thought I was being all clever by doing this:
lst = [[]] * 3
But I…
A.Wan
- 1,818
- 3
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- 34
10
votes
3 answers
What is the best approach to convert immutable objects to mutable objects (recursive)?
Specifically, this problem has come to me when I make a request with AFNeworking with JSONkit and receive a (id)JSON with several arrays and dictionaries nested.
If I don't want to modify the data, I don't have any problem:
self.myNSArray = [JSON…
martinezdelariva
- 5,011
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- 30
10
votes
3 answers
Haskell real-time update and lookup performance
I am writing a game-playing ai (aichallenge.org - Ants), which requires a lot of updating of, and referring to data-structures. I have tried both Arrays and Maps, but the basic problem seems to be that every update creates a new value, which makes…
Greg O'Keefe
- 101
- 7
10
votes
2 answers
Scala: Contains in mutable and immutable sets
I've discovered a strange behavior for mutable sets which I cannot understand:
I have a object which I want to add to a set. The equals method for the class is overridden. When I add two different objects to the set, which produces the same output…
Stefan
- 111
- 5
10
votes
1 answer
In Rust, how do I create a mutable iterator?
I'm having difficulty with lifetimes when trying to create a mutable iterator in safe Rust.
Here is what I have reduced my problem to:
struct DataStruct {
inner: Box<[T]>,
}
pub struct IterMut<'a, T> {
obj: &'a mut DataStruct,
…
Barnaby Dalton
- 158
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10
votes
4 answers
Caching expensive data in C++ - function-scoped statics vs mutable member variables
I've got a relatively expensive data-fetching operation that I want to cache the results of. This operation is called from const methods, roughly like this:
double AdjustData(double d, int key) const {
double factor =…
Dominic Rodger
- 97,747
- 36
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10
votes
1 answer
When an immutable reference to a mutable reference to a value outside the scope is returned, why is the mutable reference dropped when the scope ends?
fn main() {
// block1: fails
{
let mut m = 10;
let n = {
let b = &&mut m;
&**b // just returning b fails
};
println!("{:?}", n);
}
// block2: passes
{
let mut m =…
soupybionics
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