Bug 23400 – [REG 2.099] Can't format enum value whose base type has non-const opEquals

As of DMD 2.100.2, the following program fails to compile: --- struct flagenum { auto opEquals(typeof(this) a) { return false; } } enum foo { a = flagenum() } void main() { import std.format: formatValue, singleSpec; import std.range: nullSink; foo bar; auto spec = singleSpec("%s"); auto sink = nullSink; formatValue(sink, bar, spec); } --- The error message is: --- /usr/include/dmd/phobos/std/format/internal/write.d(3024): Error: mutable method `bug.flagenum.opEquals` is not callable using a `const` object bug.d(2): Consider adding `const` or `inout` here /usr/include/dmd/phobos/std/format/write.d(1239): Error: template instance `std.format.internal.write.formatValueImpl!(NullSink, foo, char)` error instantiating bug.d(16): instantiated from here: `formatValue!(NullSink, foo, char)` --- According to run.dlang.io, this is a regression introduced in Phobos 2.099: 2.079.1 to 2.098.1: Success and no output 2.099.1: Failure with output: ----- /path/to/dmd.linux/dmd2/linux/bin64/../../src/phobos/std/format/internal/write.d(2899): Error: mutable method `onlineapp.flagenum.opEquals` is not callable using a `const` object onlineapp.d(2): Consider adding `const` or `inout` here /path/to/dmd.linux/dmd2/linux/bin64/../../src/phobos/std/format/write.d(1239): Error: template instance `std.format.internal.write.formatValueImpl!(NullSink, foo, char)` error instantiating onlineapp.d(16): instantiated from here: `formatValue!(NullSink, foo, char)` -----

PR: https://github.com/dlang/phobos/pull/8507

Correction--this is the PR: https://github.com/dlang/phobos/pull/8591

@pbackus updated dlang/phobos pull request #8591 "Fix issue 23400 - Can't format enum value whose base type has non-con…" fixing this issue: - Fix issue 23400 - Can't format enum value whose base type has non-const opEquals https://github.com/dlang/phobos/pull/8591

dlang/phobos pull request #8591 "Fix issue 23400 - Can't format enum value whose base type has non-con…" was merged into stable: - 94fa37f2bf5aea48f83518ff58310a3b68c0a89a by Paul Backus: Fix issue 23400 - Can't format enum value whose base type has non-const opEquals https://github.com/dlang/phobos/pull/8591