http://d.puremagic.com/issues/show_bug.cgi?id=3952
--- Comment #1 from bearophile_h...@eml.cc 2010-08-06 09:34:59 PDT --- In D1 there were no template constraints, so to test the template arguments I used to add some static asserts inside them. So a wrong template argument shows a error message written by me that explains why the instantiation has failed (unfortunately those error messages show the line number inside the template). When a template constraint is composed of some different parts in &&, it's less easy to understand what condition has failed, so I miss the error messages written by me. This is an example (that probably I will simplify), there are four conditions, and for a person that has not written this code, and is just using Phobos, it's not immediately obvious what part has failed: auto opBinary(string op, TOther)(TOther other) if (op == "~" && is(TOther == struct) && (!__traits(compiles, { void isTuple(U...)(Tuple!U){} isTuple(other); }) || distinctFieldNames!(T, TOther.TypesAndStrings)() )) { ... There is a simple solution. The simple template constraints often don't need extra error messages, so they can be left as they are now. Putting one or more error message inside a template constraints turns them into messy code, so in such cases it's better to move the tests elsewhere, in an external template/CTFE: template IsGoodFoo(T) { static if (...) { enum bool IsGoodFoo = true; } else { ctputs("this is an error message"); return false; } } void foo(T)(T x) if (IsGoodFoo!T) { ... So the ctputs() is usable for the template constraints error messages too. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------