On Thursday, 1 December 2022 at 08:09:05 UTC, WebFreak001 wrote:
I've got this class definition:
```d
class X
{
this()
{
assert(false);
}
int x = 3;
}
```
due to internal reasons the constructor would fail at compile
time, so I put in an assert(false) here, and I can't add or
change any methods in X.
How do I get `3` if I have `X` and field name `"x"` at compile
time?
For structs `X.init.x` / `__traits(getMember, X.init, "x")`
would work, however for classes it complains about null
dereference.
I saw there is __traits(initSymbol), however that one doesn't
work at compile time.
AFAIK, there is no way. Unlike a struct's init symbol, a class'
one doesn't necessarily represent a valid instance state - it's
just the raw payload before invoking a ctor (which constructs a
valid instance), and the state 'dead' memory is reset to after
finalizing an object instance (to prevent dead pointers keeping
other GC refs alive).
If the ctor worked at CTFE, one could use:
```d
int get() {
scope x = new X;
return x.x;
}
enum bla = get();
```
to get the `x` value of a *valid* instance, which might be
different than the static initializer (if modified in the ctor).
I guess the main question is why do you require the static
initializers of these fields at compile-time.
`__traits(initSymbol)` was added to aid in manual blitting at
runtime.
