Bug 21705 – Nullable!T.opEquals fails for T with non-const opEquals overload

Example program: --- import std.typecons; struct S { int n; bool opEquals(S rhs) { return n == rhs.n; } } void main() { Nullable!S example = S(); S s; assert(example.opEquals(s)); } --- As of DMD 2.095.1, this program fails to compile, with the following error message: --- bug.d(13): Error: template `std.typecons.Nullable!(S).Nullable.opEquals` cannot deduce function from argument types `!()(S)`, candidates are: /usr/include/dmd/phobos/std/typecons.d(2720): `opEquals()(auto ref const(typeof(this)) rhs)` /usr/include/dmd/phobos/std/typecons.d(2730): `opEquals(U)(auto ref const(U) rhs)` with `U = S` must satisfy the following constraint: ` is(typeof(this.get == rhs))` --- Note that an explicit call to opEquals is necessary to prevent the compiler from falling back to the deprecated `alias get this`.

Another example: --- import std.typecons; struct S { int n; bool opEquals(S rhs) { return n == rhs.n; } } void main() { Nullable!S example1 = S(1), example2 = S(1); assert(example1 == example2); } --- Produces the following error message with DMD 2.095.1: --- /usr/include/dmd/phobos/std/typecons.d(2726): Error: mutable method `bug.S.opEquals` is not callable using a `const` object bug.d(6): Consider adding `const` or `inout` here bug.d(12): Error: template instance `std.typecons.Nullable!(S).Nullable.opEquals!()` error instantiating ---

@pbackus created dlang/phobos pull request #7852 "Fix Issue 21705 - Nullable!T.opEquals fails for T with non-const opEq…" fixing this issue: - Fix Issue 21705 - Nullable!T.opEquals fails for T with non-const opEquals overload https://github.com/dlang/phobos/pull/7852

dlang/phobos pull request #7852 "Fix Issue 21705 - Nullable!T.opEquals fails for T with non-const opEq…" was merged into master: - 4fb71b8c768f9afd79ca1bf73405216d0b557990 by Paul Backus: Fix Issue 21705 - Nullable!T.opEquals fails for T with non-const opEquals overload https://github.com/dlang/phobos/pull/7852