this code give error:

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

 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

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.

On Monday, 1 July 2024 at 07:32:30 UTC, Dakota wrote:

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:

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

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

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

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.

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

There is a case check will give wrong resutls:

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.

On Monday, 15 July 2024 at 06:44:12 UTC, Dakota wrote:

struct type_s
{

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

I put type_s in a file anonstruct.c, then:

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?

On Monday, 15 July 2024 at 11:16:23 UTC, Nick Treleaven wrote:

import anonstruct;

pragma(msg, isStatic!(type_s.c));

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.