• Dakota (19/19) Jul 01 this code give error:
• Nick Treleaven (10/16) Jul 01 __traits(compiles, ...) can't check if a declaration is valid
• Dakota (2/20) Jul 01 Thanks, this work for me.
• Dakota (17/18) Jul 14 There is a case check will give wrong resutls:
• Nick Treleaven (8/22) Jul 15 I put `type_s` in a file anonstruct.c, then:
• Dakota (5/12) Jul 15 No, I am here deal with a lot type and structs, no symbol problem

Dakota <dakota gmail.com> writes:

this code give error:

```d
static if(  !__traits(compiles, mixin("enum v = V;")) ) {
    enum v = V;
}

```

```sh
  Error: static variable `NotWorkVar` cannot be read at compile 
time
```

V is alias get from `typeof(__traits(getMember, M, symbol)`,  M 
is `module` from importC.


the importC source "test.h" code for `NotWorkVar`

```c
extern const float NotWorkVar;
```

I am try to ` static foreach(symbol; __traits(allMembers, 
importCModule))`,  and want to check if the symbol is `static 
variable` or not at compile time.

Nick Treleaven <nick geany.org> writes:

On Monday, 1 July 2024 at 07:32:30 UTC, Dakota wrote:
 this code give error:

 ```d
 static if(  !__traits(compiles, mixin("enum v = V;")) ) {
    enum v = V;
 }

 ```

__traits(compiles, ...) can't check if a declaration is valid 
directly. You have to wrap it in a function literal expression:
```d
enum isStatic(alias V) = __traits(compiles, { enum v = V; });

extern const float NotWorkVar;
const float Works = 2;

pragma(msg, isStatic!NotWorkVar); // false
pragma(msg, isStatic!Works); // true
```

Dakota <dakota gmail.com> writes:

On Monday, 1 July 2024 at 11:15:46 UTC, Nick Treleaven wrote:
 On Monday, 1 July 2024 at 07:32:30 UTC, Dakota wrote:
 this code give error:

 ```d
 static if(  !__traits(compiles, mixin("enum v = V;")) ) {
    enum v = V;
 }

 ```

 __traits(compiles, ...) can't check if a declaration is valid 
 directly. You have to wrap it in a function literal expression:
 ```d
 enum isStatic(alias V) = __traits(compiles, { enum v = V; });

 extern const float NotWorkVar;
 const float Works = 2;

 pragma(msg, isStatic!NotWorkVar); // false
 pragma(msg, isStatic!Works); // true
 ```

Thanks, this work for me.

Dakota <dakota gmail.com> writes:

On Monday, 1 July 2024 at 11:15:46 UTC, Nick Treleaven wrote:
 ```


There is a case check will give wrong resutls:


```d
struct type_s
{

     union {
         struct
         {
             int a;
             int b;
         } c;
     };
};
```

`type c` will return false with `enum isStatic(alias V) = 
__traits(compiles, { enum v = V; });`

type_s is from importC with DMD v2.110.0-beta.1.

Nick Treleaven <nick geany.org> writes:

On Monday, 15 July 2024 at 06:44:12 UTC, Dakota wrote:
 ```d
 struct type_s
 {

     union {
         struct
         {
             int a;
             int b;
         } c;
     };
 };
 ```

 `type c` will return false with `enum isStatic(alias V) = 
 __traits(compiles, { enum v = V; });`

I put `type_s` in a file anonstruct.c, then:
```d
import anonstruct;

pragma(msg, isStatic!(type_s.c));
```
That outputs `false`, because the symbol is not a compile-time 
value. Is that what you meant?

Dakota <dakota gmail.com> writes:

On Monday, 15 July 2024 at 11:16:23 UTC, Nick Treleaven wrote:
 I put `type_s` in a file anonstruct.c, then:
 ```d
 import anonstruct;

 pragma(msg, isStatic!(type_s.c));
 ```
 That outputs `false`, because the symbol is not a compile-time 
 value. Is that what you meant?


No, I am here deal with a lot type and structs, no symbol problem 
yet.

I guess the problem cause by the subtype has a hidden pointer to 
parent.