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digitalmars.D.learn - alias and __VERSION__ condition doesn't play well

reply frame <frame86 live.com> writes:
At the very top of my module I have this declaration:

```d
static if (__VERSION__ >= 2098)
{
     alias Foo = TypeA;
}
else
{
     alias Foo = TypeB;
}
```

No problem inside the module itself but this doesn't work when 
imported from another module:
Error: undefined identifier `Foo`

While this workaround works:

```d
template getAlias()
{
     static if (__VERSION__ >= 2098)
     {
         alias getAlias = TypeA;
     }
     else
     {
         alias getAlias = TypeB;
     }
}
alias Foo = getAlias!();
```

Is there a reason for that?
Jan 17 2022
next sibling parent vit <vit vit.vit> writes:
On Tuesday, 18 January 2022 at 04:42:45 UTC, frame wrote:

 At the very top of my module I have this declaration:

 ```d
 static if (__VERSION__ >= 2098)
 {
     alias Foo = TypeA;
 }
 else
 {
     alias Foo = TypeB;
 }
 ```

 No problem inside the module itself but this doesn't work when 
 imported from another module:
 Error: undefined identifier `Foo`

 While this workaround works:

 ```d
 template getAlias()
 {
     static if (__VERSION__ >= 2098)
     {
         alias getAlias = TypeA;
     }
     else
     {
         alias getAlias = TypeB;
     }
 }
 alias Foo = getAlias!();
 ```

 Is there a reason for that?


static ifs and mixins need semantic analysis to expand, but when 
you import module, the semantic analysis doesn't run yet (depends 
on order).

Beter workaround is:
```d
import std.traits : Select;

alias Foo  = Select!(__VERSION__ >= 2098, TypeA, TypeB);
```
Jan 17 2022
prev sibling parent reply Paul Backus <snarwin gmail.com> writes:
On Tuesday, 18 January 2022 at 04:42:45 UTC, frame wrote:

 At the very top of my module I have this declaration:

 ```d
 static if (__VERSION__ >= 2098)
 {
     alias Foo = TypeA;
 }
 else
 {
     alias Foo = TypeB;
 }
 ```

 No problem inside the module itself but this doesn't work when 
 imported from another module:
 Error: undefined identifier `Foo`


Works for me: https://run.dlang.io/is/XZlvQ8
Jan 18 2022
parent reply vit <vit vit.vit> writes:
On Tuesday, 18 January 2022 at 12:05:38 UTC, Paul Backus wrote:

 On Tuesday, 18 January 2022 at 04:42:45 UTC, frame wrote:

 At the very top of my module I have this declaration:

 ```d
 static if (__VERSION__ >= 2098)
 {
     alias Foo = TypeA;
 }
 else
 {
     alias Foo = TypeB;
 }
 ```

 No problem inside the module itself but this doesn't work when 
 imported from another module:
 Error: undefined identifier `Foo`


 Works for me: https://run.dlang.io/is/XZlvQ8


It works until you have cyclic dependencies:

https://run.dlang.io/is/wDDcK5
Jan 18 2022
parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 1/18/22 7:19 AM, vit wrote:

 On Tuesday, 18 January 2022 at 12:05:38 UTC, Paul Backus wrote:

 On Tuesday, 18 January 2022 at 04:42:45 UTC, frame wrote:

 At the very top of my module I have this declaration:

 ```d
 static if (__VERSION__ >= 2098)
 {
     alias Foo = TypeA;
 }
 else
 {
     alias Foo = TypeB;
 }
 ```

 No problem inside the module itself but this doesn't work when 
 imported from another module:
 Error: undefined identifier `Foo`


 Works for me: https://run.dlang.io/is/XZlvQ8


 
 It works until you have cyclic dependencies:
 
 https://run.dlang.io/is/wDDcK5


Has nothing to do with `__VERSION__`:

https://run.dlang.io/is/pa8lDy

That does seem like a bug. And it's LDC specific, dmd seems to work fine.

-Steve
Jan 18 2022
parent vit <vit vit.vit> writes:
On Wednesday, 19 January 2022 at 04:15:54 UTC, Steven 
Schveighoffer wrote:

 On 1/18/22 7:19 AM, vit wrote:

 On Tuesday, 18 January 2022 at 12:05:38 UTC, Paul Backus wrote:

 On Tuesday, 18 January 2022 at 04:42:45 UTC, frame wrote:

 At the very top of my module I have this declaration:

 ```d
 static if (__VERSION__ >= 2098)
 {
     alias Foo = TypeA;
 }
 else
 {
     alias Foo = TypeB;
 }
 ```

 No problem inside the module itself but this doesn't work 
 when imported from another module:
 Error: undefined identifier `Foo`


 Works for me: https://run.dlang.io/is/XZlvQ8


 
 It works until you have cyclic dependencies:
 
 https://run.dlang.io/is/wDDcK5


 Has nothing to do with `__VERSION__`:

 https://run.dlang.io/is/pa8lDy

 That does seem like a bug. And it's LDC specific, dmd seems to 
 work fine.

 -Steve


In dmd is order of module compilation different.
Same problem:

https://run.dlang.io/is/NkySAw

This is not only problem with imports:

```d
class Foo{
     Bar.B b;

     static if(true)
     	alias F = int;

}

class Bar{
     Foo.F f;     //Error: no property `F` for type `onlineapp.Foo`

     static if(true)
     	alias B = int;

}

void main(){}
```
Jan 18 2022