I wrote an AR archive (.a files) parser in D

[Paul Backus]

On Thursday, 8 August 2024 at 11:07:35 UTC, IchorDev wrote:
> On Thursday, 8 August 2024 at 10:44:49 UTC, Renato Athaydes 
> wrote:
>> Why shouldn't I cast the `read` result directly to immutable 
>> when it's literally impossible to get a reference to those 
>> bytes that is not immutable? It seems like the best way to 
>> achieve what I need.
>
> You’re still violating the guarantees of immutability—data 
> can’t go from mutable to immutable, that’s what `const` is for. 
> Using `const` would be totally fine, or you can use `.idup` to 
> create an immutable copy of the array.

Strictly speaking, you are allowed to cast from const/mutable to 
immutable if there is only one reference to the data in question:

> A memory location can be transferred from thread-local to 
> immutable or shared if there is only one reference to the 
> location.

Source: https://dlang.org/spec/intro.html#memory-model

The recommended way to do this is to use the library function 
[`assumeUnique`][1], since that communicates the intent of the 
code better than a naked cast.

[1]: https://dlang.org/library/std/exception/assume_unique.html