Bug 12166 – Template Argument Pattern Matching Fails for Struct With Multiple Nested Template Arguments

struct Zero {} struct Succ(a) {} struct Nil {} struct Cons(a, b) {} alias list1 = Cons!(Three, Cons!(Two, Cons!(Four, Cons!(One, Nil)))); alias numlHead(L: Cons!(a, b), a, b) = a; alias numlTail(L: Cons!(a, b), a, b) = b; void main() { //Error: template instance numlHead!(list1) does not //match template declaration numlHead(L : Cons!(a, b), a, b) pragma(msg, numlHead!list1); }

The test case lacks some symbols: test.d(7): Error: undefined identifier Three test.d(7): Error: undefined identifier Two test.d(7): Error: undefined identifier Four test.d(7): Error: undefined identifier One

(In reply to comment #1) > The test case lacks some symbols: > > test.d(7): Error: undefined identifier Three > test.d(7): Error: undefined identifier Two > test.d(7): Error: undefined identifier Four > test.d(7): Error: undefined identifier One Sorry, add: alias One = Succ!Zero; alias Two = Succ!One; alias Three = Succ!Two; alias Four = Succ!Three;

(In reply to comment #2) > Sorry, add: [snip] So, what version do you use? The full test case: struct Zero {} struct Succ(a) {} alias One = Succ!Zero; alias Two = Succ!One; alias Three = Succ!Two; alias Four = Succ!Three; struct Nil {} struct Cons(a, b) {} alias list1 = Cons!(Three, Cons!(Two, Cons!(Four, Cons!(One, Nil)))); alias numlHead(L: Cons!(a, b), a, b) = a; alias numlTail(L: Cons!(a, b), a, b) = b; void main() { pragma(msg, numlHead!list1); } compiles with 2.064 (2.063 and earlier does not support new alias syntax). I cannot see the issue.

(In reply to comment #3) > (In reply to comment #2) > > Sorry, add: > [snip] > > So, what version do you use? The full test case: > > struct Zero {} > struct Succ(a) {} > > alias One = Succ!Zero; > alias Two = Succ!One; > alias Three = Succ!Two; > alias Four = Succ!Three; > > struct Nil {} > struct Cons(a, b) {} > > alias list1 = Cons!(Three, Cons!(Two, Cons!(Four, Cons!(One, Nil)))); > > alias numlHead(L: Cons!(a, b), a, b) = a; > > alias numlTail(L: Cons!(a, b), a, b) = b; > > void main() > { > pragma(msg, numlHead!list1); > } > > compiles with 2.064 (2.063 and earlier does not support new alias syntax). I > cannot see the issue. It seems it was an error on my part. In the full code, I had some testing code in my main method. I accidentally named a variable list1 as well as having the list1 alias, so my code broke with this: void main() { //assert(is(Four == Succ!(Succ!(Succ!(Succ!Zero))))); auto list1 = list1(); //Problem //assert(is(typeof(three) == Three)); //assert(numValue!(Number!Zero) == 0); assert(numValue!(Number!Four) == 4); pragma(msg, numlHead!list1); //assert(is(numlHead!list1 == Three)); //assert(is(typeof(numlTail!list1) == Cons!(Two, Cons!Four, Cons!(One, Nil)))); } However, it also seems this is bad behaviour. Should I open a separate report?

(In reply to comment #4) > However, it also seems this is bad behaviour. Shadowing *module level* symbols by declared local symbols is legitimate. Currently there's no plan to disallow it, and I also think it should be continuously allowed. > Should I open a separate report? However of course, it's your free.