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digitalmars.D.announce - DIP1046, "ref For Variable Declarations", has been Accepted

reply Mike Parker <aldacron gmail.com> writes:
DIP1046, "ref For Variable Declarations", has been accepted:

https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1046.md

Under the new DIP process, any DIP written by one of the language 
maintainers has an extra step to go through once it's ready to 
leave the DIP Development forum and enter into Formal Assessment: 
it must first be discussed at a DLF meeting to determine if there 
are any major objections that should block its approval. If there 
are none, then the other language maintainer is free to review 
the DIP and render a final verdict. Otherwise, further discussion 
and debate is undertaken to determine how to proceed.

Since Walter is the author of DIP1046, I presented it at a 
meeting for which the following members were present:

Jonathan M. Davis
Timon Gehr
Martin Kinkelin
Dennis Korpel
Mathias Lang
Mike Parker
Robert Schadek
Steven Schveighoffer
Adam Wilson

None of the members raised any objections to block its approval. 
I then submitted it to Átila for review. He requested a 
clarification, which Walter made, and then approved it. He agreed 
with the DIP's rationale that ref declarations are a major tool 
for writing memory-safe code and believes they align with our 
overarching goal of enhancing memory safety in D.

In contrast, Walter's bitfields DIP, [currently in its third 
draft](https://forum.dlang.org/post/v193hc$b9c$1 digitalmars.com), was
presented at the same meeting and received major objections. I'll have a report
on how we decided to proceed when I post the update for that meeting.
Jun 23
parent reply Vladimir Marchevsky <vladimmi gmail.com> writes:
On Sunday, 23 June 2024 at 13:29:21 UTC, Mike Parker wrote:

 DIP1046, "ref For Variable Declarations", has been accepted:

 https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1046.md



 which reduces the complexity of the code, as long-winded global 
 names get a shorthand


Does ref add anything compared to using an alias?..
Jun 23
next sibling parent Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Sunday, June 23, 2024 3:50:37 PM MDT Vladimir Marchevsky via Digitalmars-d-
announce wrote:

 On Sunday, 23 June 2024 at 13:29:21 UTC, Mike Parker wrote:

 DIP1046, "ref For Variable Declarations", has been accepted:

 https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1046.md

 which reduces the complexity of the code, as long-winded global
 names get a shorthand


 Does ref add anything compared to using an alias?..


alias allows you to give a symbol another name (essentially resulting in the
compiler replacing the new name with the original name anywhere that it sees
it), whereas ref involves taking the address of a variable - just like a
pointer except that it's automatically dereferenced for you, and since the
compiler controls the creation of ref (vs being able to take the address of
pretty much anything to create a pointer), it can be  safe as a result. So,
you can think of ref as being an  safe pointer (and what can be done with it
is more restricted in order to be able to guarantee that it's  safe). This
DIP expands the use of ref so that there are more places where we can use
it, whereas before, those cases would have required pointers and likely
would have required  trusted on code that took the address to create the
pointer in order for the code to be  safe.

https://dlang.org/spec/declaration.html#alias

https://dlang.org/spec/declaration.html#ref-storage

While alias can be used on symbols such as variables, it's usually used on
types (similar to C/C++'s typedef), whereas ref can only be used on
variables.

- Jonathan M Davis
Jun 23
prev sibling parent reply Nick Treleaven <nick geany.org> writes:
On Sunday, 23 June 2024 at 21:50:37 UTC, Vladimir Marchevsky 
wrote:

 On Sunday, 23 June 2024 at 13:29:21 UTC, Mike Parker wrote:

 DIP1046, "ref For Variable Declarations", has been accepted:

 https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1046.md



 which reduces the complexity of the code, as long-winded 
 global names get a shorthand


 Does ref add anything compared to using an alias?..


`ref` will bind to lvalue expressions, e.g (from the DIP):

```d
ref int dark(ref int x, int i, int* q)
{
     ref m = *q;    // m refers to whatever q points to
     ...
}
```

`*q` is an expression, not a symbol. `ref` can bind to e.g. a 
struct field runtime value, or an lvalue returned from a function.

`alias` only allows giving new names for existing compile-time 
symbols.
Jun 24
parent Mike Shah <mshah.475 gmail.com> writes:
On Monday, 24 June 2024 at 11:08:32 UTC, Nick Treleaven wrote:

 On Sunday, 23 June 2024 at 21:50:37 UTC, Vladimir Marchevsky 
 wrote:

 On Sunday, 23 June 2024 at 13:29:21 UTC, Mike Parker wrote:

 [...]



 [...]


 Does ref add anything compared to using an alias?..


 `ref` will bind to lvalue expressions, e.g (from the DIP):

 ```d
 ref int dark(ref int x, int i, int* q)
 {
     ref m = *q;    // m refers to whatever q points to
     ...
 }
 ```

 `*q` is an expression, not a symbol. `ref` can bind to e.g. a 
 struct field runtime value, or an lvalue returned from a 
 function.

 `alias` only allows giving new names for existing compile-time 
 symbols.


This is welcoming news! A nice addition for folks transitioning 
over from C++ who are use to having this functionality.
Jun 24