Re: Checking for manifest constants

[Petar via Digitalmars-d-learn]

On Friday, 5 March 2021 at 08:23:09 UTC, Bogdan wrote:
I was using a trick with dmd to check for manifest constants 
which worked until dmd v2.094. Yesterday I tried it on the 
latest compiler and it failed with:


source/introspection/manifestConstant.d(37,28): Error: need 
this for name of type string
source/introspection/type.d(156,13): Error: value of this is 
not known at compile time

any ideas how to fix it? or, is it a bug with dmd?

```

/// Check if a member is manifest constant
bool isManifestConstant(T, string name)() {
  mixin(`return is(typeof(T.init.` ~ name ~ `)) && 
!is(typeof(&T.init.` ~ name ~ `));`);
}

/// ditto
bool isManifestConstant(alias T)() {
  return is(typeof(T)) && !is(typeof(&T));
}

enum globalConfig = 32;
int globalValue = 22;

unittest {
  struct Test {
    enum config = 3;
    int value = 2;
  }

  static assert(isManifestConstant!(Test.config));
  static assert(isManifestConstant!(Test, "config"));
  static assert(isManifestConstant!(globalConfig));

  static assert(!isManifestConstant!(Test.value));
  static assert(!isManifestConstant!(Test, "value"));
  static assert(!isManifestConstant!(globalValue));
}

void main() {}


```

I suggest this:

    enum globalConfig = 32;
    int globalValue = 22;
    immutable globaImmutablelValue = 22;

    enum isManifestConstant(alias symbol) =
      __traits(compiles, { enum e = symbol; }) &&
      !__traits(compiles, { const ptr = &symbol; });

    unittest {
      struct Test {
        enum config = 3;
        int value = 2;
      }

      static assert(isManifestConstant!(Test.config));
      static assert(isManifestConstant!(mixin("Test.config")));

      static assert(isManifestConstant!(globalConfig));
      static assert(isManifestConstant!(mixin("globalConfig")));

      static assert(!isManifestConstant!(Test.value));
      static assert(!isManifestConstant!(mixin("Test.value")));

      static assert(!isManifestConstant!(globalValue));
      static assert(!isManifestConstant!(mixin("globalValue")));

      static assert(!isManifestConstant!(globaImmutablelValue));
      static 
assert(!isManifestConstant!(mixin("globaImmutablelValue")));
    }