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digitalmars.D - Libdparse needs to be updated to recognize AliasAssign declarations

reply RazvanN <razvan.nitu1305 gmail.com> writes:
Hello fellow D people,

Is there anyone in the community sufficiently familiar with 
libdparse [1] as to make it recognize an AliasAssign declaration 
[2]? Andralex has made a series of PRs to phobos that make use of 
the new technology. As a result the code is greatly simplified 
[3] and it comes with some memory savings [4]. However, these PRs 
are blocked because of the style checker that does not recognize 
alias assignments.

If anyone with some experience with the libdparse repo would be 
able to fix this, that would be greatly appreciated!

Cheers,
RazvanN

[1] https://github.com/dlang-community/libdparse
[2] https://github.com/dlang/dmd/pull/11846
[3] https://github.com/dlang/phobos/pull/8040
[4] https://github.com/dlang/phobos/pull/8033
May 04 2021
parent reply WebFreak001 <d.forum webfreak.org> writes:
On Tuesday, 4 May 2021 at 12:10:55 UTC, RazvanN wrote:

 Hello fellow D people,

 Is there anyone in the community sufficiently familiar with 
 libdparse [1] as to make it recognize an AliasAssign 
 declaration [2]? Andralex has made a series of PRs to phobos 
 that make use of the new technology. As a result the code is 
 greatly simplified [3] and it comes with some memory savings 
 [4]. However, these PRs are blocked because of the style 
 checker that does not recognize alias assignments.

 If anyone with some experience with the libdparse repo would be 
 able to fix this, that would be greatly appreciated!

 Cheers,
 RazvanN

 [1] https://github.com/dlang-community/libdparse
 [2] https://github.com/dlang/dmd/pull/11846
 [3] https://github.com/dlang/phobos/pull/8040
 [4] https://github.com/dlang/phobos/pull/8033


This code is fairly clear:
```d
alias A = B;
A = C;
```

however what about this code?
```d
void foo() {
     alias A = B;
     A = C;
}
```

is the `A = C` in this case an AliasAssign? how would the parser 
differentiate between this AliasAssign and regular assignments?
May 04 2021
parent reply Paul Backus <snarwin gmail.com> writes:
On Tuesday, 4 May 2021 at 14:07:47 UTC, WebFreak001 wrote:

 however what about this code?
 ```d
 void foo() {
     alias A = B;
     A = C;
 }
 ```

 is the `A = C` in this case an AliasAssign? how would the 
 parser differentiate between this AliasAssign and regular 
 assignments?


AliasAssign is only allowed in declaration contexts--the top 
level of a module, or the body of a `struct`, `class`, 
`template`, etc. In these contexts, a normal assignment statement 
is not allowed, so there is no ambiguity.

Personally I think this is kind of a hack, and would have 
preferred a separate "rebind" operator to disambiguate (maybe 
`:=`). But this is the solution Walter decided on.
May 04 2021
next sibling parent reply WebFreak001 <d.forum webfreak.org> writes:
On Tuesday, 4 May 2021 at 14:12:28 UTC, Paul Backus wrote:

 On Tuesday, 4 May 2021 at 14:07:47 UTC, WebFreak001 wrote:

 however what about this code?
 ```d
 void foo() {
     alias A = B;
     A = C;
 }
 ```

 is the `A = C` in this case an AliasAssign? how would the 
 parser differentiate between this AliasAssign and regular 
 assignments?


 AliasAssign is only allowed in declaration contexts--the top 
 level of a module, or the body of a `struct`, `class`, 
 `template`, etc. In these contexts, a normal assignment 
 statement is not allowed, so there is no ambiguity.

 Personally I think this is kind of a hack, and would have 
 preferred a separate "rebind" operator to disambiguate (maybe 
 `:=`). But this is the solution Walter decided on.


in that case that will make it easy to add it to libdparse
May 04 2021
parent RazvanN <razvan.nitu1305 gmail.com> writes:
On Tuesday, 4 May 2021 at 14:18:33 UTC, WebFreak001 wrote:

 On Tuesday, 4 May 2021 at 14:12:28 UTC, Paul Backus wrote:

 On Tuesday, 4 May 2021 at 14:07:47 UTC, WebFreak001 wrote:





 in that case that will make it easy to add it to libdparse


I have made an attempt, if anyone is willing to review: 
https://github.com/dlang-community/libdparse/pull/441
May 06 2021
prev sibling parent reply user1234 <user1234 12.de> writes:
On Tuesday, 4 May 2021 at 14:12:28 UTC, Paul Backus wrote:

 On Tuesday, 4 May 2021 at 14:07:47 UTC, WebFreak001 wrote:

 however what about this code?
 ```d
 void foo() {
     alias A = B;
     A = C;
 }
 ```

 is the `A = C` in this case an AliasAssign? how would the 
 parser differentiate between this AliasAssign and regular 
 assignments?


 AliasAssign is only allowed in declaration contexts--the top 
 level of a module, or the body of a `struct`, `class`, 
 `template`, etc. In these contexts, a normal assignment 
 statement is not allowed, so there is no ambiguity.


Am i wrong to think that even without this rule the difference 
could be made during semantic by testing if the assign lhs is an 
alias ?
May 04 2021
parent reply Paul Backus <snarwin gmail.com> writes:
On Tuesday, 4 May 2021 at 18:48:21 UTC, user1234 wrote:

 Am i wrong to think that even without this rule the difference 
 could be made during semantic by testing if the assign lhs is 
 an alias ?


That would break existing code. For example:

     void main() {
         int x = 123;
         int y = 456;
         alias z = x;
         z = y; // runtime assignment
         assert(x == 456);
     }
May 04 2021
parent reply user1234 <user1234 12.de> writes:
On Tuesday, 4 May 2021 at 18:59:05 UTC, Paul Backus wrote:

 On Tuesday, 4 May 2021 at 18:48:21 UTC, user1234 wrote:

 Am i wrong to think that even without this rule the difference 
 could be made during semantic by testing if the assign lhs is 
 an alias ?


 That would break existing code. For example:

     void main() {
         int x = 123;
         int y = 456;
         alias z = x;
         z = y; // runtime assignment
         assert(x == 456);
     }


You can make the difference tho. z is not a type or a 
compile-time sequence.
May 04 2021
parent reply Paul Backus <snarwin gmail.com> writes:
On Tuesday, 4 May 2021 at 19:04:59 UTC, user1234 wrote:

 On Tuesday, 4 May 2021 at 18:59:05 UTC, Paul Backus wrote:

 That would break existing code. For example:

     void main() {
         int x = 123;
         int y = 456;
         alias z = x;
         z = y; // runtime assignment
         assert(x == 456);
     }


 You can make the difference tho. z is not a type or a 
 compile-time sequence.


AliasAssign is not limited to just types and compile-time 
sequences, so I don't see why that's relevant.
May 04 2021
parent user1234 <user1234 12.de> writes:
On Tuesday, 4 May 2021 at 19:21:36 UTC, Paul Backus wrote:

 On Tuesday, 4 May 2021 at 19:04:59 UTC, user1234 wrote:

 On Tuesday, 4 May 2021 at 18:59:05 UTC, Paul Backus wrote:

 That would break existing code. For example:

     void main() {
         int x = 123;
         int y = 456;
         alias z = x;
         z = y; // runtime assignment
         assert(x == 456);
     }


 You can make the difference tho. z is not a type or a 
 compile-time sequence.


 AliasAssign is not limited to just types and compile-time 
 sequences,


Ah yes, this is why I thought it was possible.


 so I don't see why that's relevant.
May 05 2021