// parse.d parseInterpolatedString
auto exp = new AST.TupleExp(token.loc, parts);
AST.Expression e = new AST.IdentifierExp(exp.loc, Id.empty);
e = new AST.DotIdExp(exp.loc, e, Id.object);
e = new AST.DotIdExp(exp.loc, e, Identifier.idPool("_interpolation"));
return new AST.CallExp(exp.loc, e, exp);

// object.d
struct Interpolation(T...) {

  immutable T args;

  private this()(auto ref T args) { this.args = args; }
  @disable this(this);

  string toString() { return from!q{std.conv}.text(args); }
  alias toString this;

}

auto _interpolation(T...)(auto ref T args)
  if (T.length > 0) { return Interpolation!T(args); }