Bug 9580 – std.variant.Algebraic with Tuple format problem

import std.variant: Algebraic, This; import std.typecons: Tuple; alias Foo = Algebraic!(int, Tuple!(This[])); void main() { auto f = Foo(0); } DMD 2.063alpha gives: ...\dmd2\src\phobos\std\format.d(1821): Error: static assert (isInputRange!(This[])) is false ...\dmd2\src\phobos\std\format.d(2279): instantiated from here: formatValue!(Appender!(string), This[], char) ...\dmd2\src\phobos\std\typecons.d(551): instantiated from here: formatElement!(Appender!(string), This[], char) temp.d(3): instantiated from here: Tuple!(This[])

I'm on the road now but a quick test suggests that simply providing an empty definition for This fixes the problem: struct This {} Can someone give it a shot?

Now the original code compiles with no errors. But if I try to to instantiate a Foo that contains an array of Foos: import std.variant: Algebraic, This; import std.typecons: Tuple; alias Foo = Algebraic!(int, Tuple!(This[])); void main() { auto f = Foo(0); auto f = Foo([Foo(0)]); } I see (dmd 2.065alpha): ...\dmd2\src\phobos\std\variant.d(548): Error: static assert "Cannot store a VariantN!(8u, int, Tuple!(This[]))[] in a VariantN!(8u, int, Tuple!(This[]))" temp.d(6): instantiated from here: __ctor!(VariantN!(8u, int, Tuple!(This[]))[])

Sorry, the code in comment2 is wrong. This should be better: import std.variant: Algebraic, This; import std.typecons: Tuple, tuple; alias Foo = Algebraic!(int, Tuple!(This[])); void main() { auto f = Foo(tuple([Foo(0)])); } The error messages: ...\dmd2\src\phobos\std\variant.d(548): Error: static assert "Cannot store a Tuple!(VariantN!(8u, int, Tuple!(This[]))[]) in a VariantN!(8u, int, Tuple!(This[]))" temp.d(5): instantiated from here: __ctor!(Tuple!(VariantN!(8u, int, Tuple!(This[]))[]))

The code in comment 3 compiles great on 2.070. The problem seems to have been solved at some point since new year 2014.