On Tuesday, 20 February 2018 at 16:12:17 UTC, Adam D. Ruppe wrote:
On Monday, 19 February 2018 at 08:28:22 UTC, aliak wrote:
T is the wrapped type. So if T has a member (in the example it's the built in field "max") then forward that.

Oh, I see what you mean.

So the problem is that built in types don't have "members" per se, they have "magic". The built in properties don't count to `hasMember`. You could probably do `if(__traits(compiles, mixin("a." ~ member))` though.

I assume this should work because rules for alias this (as I understand) are to basically try if there's a member name that resolves the call, else forward to alias this.

yeah, just built in properties/members don't pass the same existence checks so that's confusing your template constraint.

I believe the same happens if it's not a built in property. You can replace B!int with B!S and have S contains a function "f" (for instance), then whether or the not constraint on opDispatch is:

__traits(compiles, mixin("t." ~ name))
hasMember(T, name)

You still get:

b.p.writeln; // Error: no property 'p' for type 'B!(S)'

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