Template constraint on alias template parameter.

jmh530 john.michael.hall at gmail.com
Thu Aug 6 16:01:35 UTC 2020

The code below compiles, but I want to put an additional 
constraint on the `test` function is only called with a Foo 

I tried things like is(T == Foo) and is(T : Foo), but those don't 
work. However, something like is(T!int : Foo!int) works, but 
is(T!U == Foo!U, U) doesn't. Any idea why is(T!U == Foo!U, U) 
doesn't work?

struct Foo(T)
     T x;

void test(alias T)()
     if (__traits(isTemplate, T))
     import std.stdio: writeln;

void main()

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