import std.algorithm;

auto fun(T)(T a){return a;}

template fun2(T){auto fun2(T a){return fun(a);}}//OK but heavy syntax and cannot be nested inside test()

void main(){

  //alias fun2=fun!int; //OK but needs to specify template params

  //none of those work:

  //alias fun2=a=>fun(a);

  //alias fun2(T)=(T a)=>fun(a);

  //alias fun2(T)=(T a){return fun(a);}

  auto b=[1].map!fun2;

  assert(b.equal([1]));

}