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
27
votes
4 answers
Cannot obtain a mutable reference when iterating a recursive structure: cannot borrow as mutable more than once at a time
I'm trying to navigate a recursive data structure iteratively in order to insert elements at a certain position. To my limited understanding, this means taking a mutable reference to the root of the structure and successively replacing it by a…
Fabian Knorr
- 3,134
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27
votes
8 answers
Why the "mutable default argument fix" syntax is so ugly, asks python newbie
Now following my series of "python newbie questions" and based on another question.
Prerogative
Go to http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#other-languages-have-variables and scroll down to "Default Parameter Values".…
cregox
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27
votes
4 answers
Scala immutable map, when to go mutable?
My present use case is pretty trivial, either mutable or immutable Map will do the trick.
Have a method that takes an immutable Map, which then calls a 3rd party API method that takes an immutable Map as well
def doFoo(foo: String = "default",…
virtualeyes
- 11,147
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25
votes
3 answers
Loading a resource to a mutable bitmap
I am loading a bitmap from a resource like so:
Bitmap mBackground = BitmapFactory.decodeResource(res,R.drawable.image);
What I want to do is make some changes to the bitmap before It gets drawn to the main canvas in my draw method (As it would…
stealthcopter
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25
votes
1 answer
How do I pass a reference to mutable data in Rust?
I want to create a mutable struct on the stack and mutate it from helper functions.
#[derive(Debug)]
struct Game {
score: u32,
}
fn addPoint(game: &mut Game) {
game.score += 1;
}
fn main() {
let mut game = Game { score: 0 };
…
Wilfred Hughes
- 29,846
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25
votes
5 answers
Why is a string key for a hash frozen?
According to the specification, strings that are used as a key to a hash are duplicated and frozen. Other mutable objects do not seem to have such special consideration. For example, with an array key, the following is possible.
a = [0]
h = {a =>…
sawa
- 165,429
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25
votes
9 answers
Why are Java wrapper classes immutable?
I know the usual reasons that apply to general immutable classes, viz
can not change as a side effect
easy to reason about their state
inherently thread safe
no need to provide clone/copy constructor/factory copy method
instance caching
no need…
shrini1000
- 7,038
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24
votes
2 answers
Why do C# Arrays use a reference type for Enumeration, but List uses a mutable struct?
From what I've read, a design decision was made for certain Collections's Enumerator Types to be mutable structs instead of reference types for performance reasons. List.Enumerator is the most well known.
I was investigating some old code that used…
Chuu
- 4,301
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23
votes
4 answers
How to use mutable collections in Scala
I think I may be failing to understand how mutable collections work. I would expect mutable collections to be affected by applying map to them or adding new elements, however:
scala> val s: collection.mutable.Seq[Int] = collection.mutable.Seq(1)
s:…
Henry Henrinson
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22
votes
2 answers
Converting immutable to mutable collections
What is the best way to convert collection.immutable.Set to collection.mutable.Set?
barroco
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22
votes
2 answers
Convert immutable Bitmap file to mutable Bitmap
A:
Bitmap immutableBmp= BitmapFactory.decodeResource(getApplicationContext().getResources(),R.drawable.sample);
mutableBitmap=immutableBmp.copy(Bitmap.Config.ARGB_8888, true);
B:
Bitmap immutableBmp=…
Alex
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21
votes
3 answers
mutable fields in Julia struct
I couldn't find an answer in both stackoverflow and the Julia docs to the following "design problem":
Let's say I want to define the following object
struct Person
birthplace::String
age::Int
end
Since Person is immutable, I'm happy that nobody can…
stefabat
- 437
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20
votes
2 answers
Why is MutableString deprecated in Python?
Why was the MutableString class deprecated in Python 2.6;
and why was it removed in Python 3?
fjsj
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20
votes
4 answers
Why does capturing a mutable struct variable inside a closure within a using statement change its local behavior?
Update: Well, now I've gone and done it: I filed a bug report with Microsoft about this, as I seriously doubt that it is correct behavior. That said, I'm still not 100% sure what to believe regarding this question; so I can see that what is…
Dan Tao
- 125,917
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20
votes
5 answers
Passing parameters to lambda in C++
I seems to miss some point in lambda mechanism in C++. Here is the code:
std::vector vec (5);
int init = 0;
std::generate(begin(vec), end(vec), [init]() mutable { return ++init; });
for (auto item : vec) {
std::cout << item << "…
IgorStack
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