On Tuesday, 6 March 2018 at 13:56:30 UTC, Steven Schveighoffer wrote:
On 3/6/18 8:42 AM, Simen Kjærås wrote:
unittest {
     int i = 0;
     struct S {
         int n;
         void fun() const {
     const S s;
     assert(i == 0);
     assert(i == 1);

That, I would consider a bug. If it's not, then definitely, you should be able to implicitly cast to/from const.

So a bug report is in order. It should be decided one way or another -- either the context pointer is part of the struct type or it isn't.

immutable throws a wrench in the works for the idea that the context pointer is part of the struct. Consider the exact same example, but with immutable(S) instead of const(S). IMO, this indicates the context is not part of the struct (though the context *pointer* arguably is).

And just in case anyone doesn't immediately see how even disallowing the above would not solve the immutable problem:

unittest {
    int n = 0;
    struct S {
        int fun() const { return n; }
    immutable S s;
    assert(s.fun == 0);
    assert(s.fun == 1); // Not so immutable now, are you?

Interestingly, replacing 'const' with 'immutable' on fun gives a compilation error: "immutable function 'foo.__unittest_foo_1_0.S.fun' cannot access mutable data 'n'".

This seems even weirder to me, but can certainly be taken as evidence in favor of your view. The same error message does *not* show up if n is instead a global variable.


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