On Thursday, 24 September 2020 at 11:15:11 UTC, ddcovery wrote:
[...]
Example: I tried with a global function
Dot!R dt(alias fun, T, R)(Dot!T t){
auto f = cast(R function(T)) unaryFun!fun;
return t.dot!R(f);
}
[...]
the problem is the template can't automatically determine the
type "R". All the template parameters need to be resolvable from
the arguments you pass into it, R is something magic where it
doesn't know where it comes from.
To keep the R like you want to right now you can do the following:
Dot!(typeof(unaryFun!fun(T.init))) dt(alias fun, T)(Dot!T t){
return t.dot(t => unaryFun!fun(t));
}
or
Dot!R dt(alias fun, T, R = typeof(unaryFun!fun(T.init)))(Dot!T t){
return t.dot(t => unaryFun!fun(t));
}
Note that this might instantiate unaryFun twice though. The
second alternative here allows users to overwrite R and just
provides a default (might have useful use cases too)
Alternatively a lot easier would be to just return auto and do:
auto dt(alias fun, T)(Dot!T t){
return t.dot(t => unaryFun!fun(t));
}
This doesn't allow users to overwrite the return type exactly but
it simplifies implementation and doesn't look like it would
generate any double instantiation.
