How do I make a template function that only accepts instances of a specific class?

[Adam D. Ruppe]

On Monday, 18 January 2021 at 19:34:52 UTC, Jack wrote:
> is that sytax derived from there?

sort of. it is the type pattern matching "is expression" 
described here:

https://dlang.org/spec/expression.html#IsExpression

The is(A:B) thing technically means "if A is implicitly 
convertible to B" which of course works for base classes and 
interfaces well but that's not all it does, like is(int : long) 
passes too.

I just remember the syntax thanks to its similarity to type 
declarations.