Template constraint on alias template parameter.
anonymous at example.com
Thu Aug 6 18:09:50 UTC 2020
On Thursday, 6 August 2020 at 16:01:35 UTC, jmh530 wrote:
> 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()
`is(...)` only works on types. You're looking for
`__traits(isSame, T, Foo)`.
For `is(T!U == Foo!U, U)` to work, the compiler would have to
guess U. If the first guess doesn't work, it would have to guess
again, and again, and again, until it finds a U that does work.
Could take forever.
More information about the Digitalmars-d-learn