On Thu, Oct 29, 2020 at 04:56:46PM +0000, IGotD- via Digitalmars-d-learn wrote:
> On Thursday, 29 October 2020 at 16:45:51 UTC, Ali Çehreli wrote:
> >
> > import std;
> >
> > immutable string p;
> >
> > shared static this() {
> > p = environment["PATH"]; // <-- Run time
> > }
> >
>
> Just to clarify, immutable is allowed to be initialized in ctors but
> not anything later than that? Moving p = environment["PATH"] to main
> would generate an error.
1) Module-level immutable can be initialized either as part of the
declaration:
immutable int x = 1;
2) Or from inside a shared static this():
immutable int x;
shared static this() {
x = 2;
}
Note that initialization from ctor must be done from `shared static
this()`, which is global; initialization from `static this` is currently
accepted but deprecated, because that's a TLS ctor, and immutables are
implicitly shared so you could potentially break immutability by having
the TLS ctor set it to a different value per thread. Eventually this
will become a hard error.
The following are errors:
3)
immutable int x = 1;
shared static this() {
x = 2; // NG: cannot modify immutable
}
4)
immutable int x;
void main() {
x = 3; // NG: cannot modify immutable
}
T
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