I'm experiencing an error when instantiating SumType with an aggregate template that itself is instantiated with a void function. In other words...

struct Foo(alias f) {}
// As the error implies, altering it to be non-void makes everything copacetic~
void bar() {}
alias S = SumType!(Foo!bar);

The error in question...

Error: variable `std.typecons.ReplaceTypeUnless!(isSumTypeInstance, This, SumType!(Foo!(bar)), Foo!(bar)).F!(bar).replaceTemplateArgs` type `void` is inferred from initializer `bar()`, and variables cannot be of type `void`

Perhaps I'm dong something stupid, or failing to realize, because all the glue sniffing I did when I was younger has finally manifested itself, but if it's not, is there a workaround?

On Monday, 20 September 2021 at 11:21:28 UTC, surlymoor wrote:

Error: variable `std.typecons.ReplaceTypeUnless!(isSumTypeInstance, This, SumType!(Foo!(bar)), Foo!(bar)).F!(bar).replaceTemplateArgs` type `void` is inferred from initializer `bar()`, and variables cannot be of type `void`

Looks like this is a bug in ReplaceType:

import std.typecons;

struct Foo(alias f) {}
void bar() {}
alias _ = ReplaceType!(int, int, Foo!bar);

I've submitted a bug report here: https://issues.dlang.org/show_bug.cgi?id=22325

On Monday, 20 September 2021 at 15:33:23 UTC, Paul Backus wrote:

Error: variable `std.typecons.ReplaceTypeUnless!(isSumTypeInstance, This, SumType!(Foo!(bar)), Foo!(bar)).F!(bar).replaceTemplateArgs` type `void` is inferred from initializer `bar()`, and variables cannot be of type `void`

import std.typecons;

struct Foo(alias f) {}
void bar() {}
alias _ = ReplaceType!(int, int, Foo!bar);

Thanks, Paul. Glad to see the fix is simple.