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Why are immutable structs default in Julia?

By : tholin
Date : September 08 2020, 09:00 PM
this one helps. This is discussed in this PR to Julia. I'll just quote from Jeff Bezanson:
We should steer people to immutable types by default. Immutable is generally better and faster, has better default behavior with ===, and it's really pretty rare to need to update object fields. Base has many more immutable types than mutable, and in making this change it seemed to me that even more types could be made immutable. But type Foo looks more natural than immutable Foo, so type tends to be the default choice. This change reverses that, with struct Foo being more natural, and immutable. Writing mutable struct Foo makes you ask "does this really need to be mutable?", which is a good thing! Immutable struct types are the closest thing we have to value type structs in other languages. We inline them in arrays in at least some cases, and being immutable makes it much harder to tell whether they are value or reference types. FWIW, Rust also uses struct and makes them immutable. Not that we need to copy Rust, but it adds confidence that this is a reasonable thing to do.
code :

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Should structs always be immutable?

By : Dave McRae
Date : March 29 2020, 07:55 AM
I hope this helps . A phone number does not change; you just get a different one and discard the old one. The old one is still the same it always was. Same with dates, numbers, etc. - think of this when approaching structs. They are a way to encapsulate a value - which simply is; not the usage of the value, which changes.

Why are C# structs immutable?

By : user2311137
Date : March 29 2020, 07:55 AM
I wish did fix the issue. If this subject interests you, I have a number of articles about immutable programming at http://blogs.msdn.com/b/ericlippert/archive/tags/immutability/
code :
void M()
    S s = whatever;
    ... lots of code ...
    ... lots more code ...
void Helper(S s)
    ... lots of code ...
    ... lots more code ...
public static File OpenFile(string filename)
    if (!HasPermission(filename)) throw new SecurityException();
    return InternalOpenFile(filename);

.NET ORMs, immutable value objects, structs, default constructors, and readonly properties

By : Oswald
Date : March 29 2020, 07:55 AM
I wish did fix the issue. As the comments point out, you will have to make some compromises when/if you adopt an ORM. The thing to remember in my opinion is that the gains in productivity far outweigh the "costs" of these compromises.
I did want to point out to you (since you're new to EF) that you can customize the T4 templates that generate EF entities and contexts. I think if you play around with this, you can iron out most of the things you don't like.

d2: Immutable structs with opApply do not compile when initialized with non-default constructor

By : Nikhil Sk
Date : March 29 2020, 07:55 AM
I wish did fix the issue. Actually, at least using DMD version 2.059, it doesn't compile (tested on Windows 7 and FreeBSD) with either constructor.
The reason for this ought to be fairly obvious. By making a struct (or class) immutable, you are simply applying immutable to every member of that struct (or class). However, the constructors do not become immutable. That is, when when you declare immutable struct Test you have effectively done the following:
code :
struct Test {
    this(int foo) { }
    immutable int opApply(int delegate(ref int) dg) {
        return (0);
struct Test {
    // Anything that needs to be mutable should go up here
    int opApply(int delegate(ref uint) dg) {
        return 0;

    // Anything put in this block is immutable
    immutable {
        this(int foo) { }

Are immutable julia structs ever safe to mutate and under what conditions can it be done in safe way?

By : Prashant Pratap Sing
Date : October 04 2020, 10:00 PM
I hope this helps you . If you modify the language implementation in way to allow breaking the rules of the language as specified, you can do whatever you want. However:
The language you're working with is no longer Julia, and Whatever changes you make may introduce bugs. If you add backdoors to allow violation of constraints of the original language, you may very well find that other parts of the language implementation that you haven't yet examined are making use of invariants depending on those language constraints, and that, without making significant changes elsewhere, your changes end up being bugs.
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