diff --git a/source/cipher.d b/source/cipher.d
index ca470b2..96a73c4 100644
--- a/source/cipher.d
+++ b/source/cipher.d
@@ -14,11 +14,8 @@ enum Cipher
     chacha20
 }
 
-mixin(cipherFunctionString.format(q{InputRange},
-                                  q{isInputRange!R && !(isForwardRange!R)}));
-
-mixin(cipherFunctionString.format(q{ForwardRange},
-                                  q{isForwardRange!R}));
+mixin(cipherFunctionString!(InputRange, isOnlyInputRange));
+mixin(cipherFunctionString!(ForwardRange, isForwardRange));
 
 unittest
 {
@@ -37,9 +34,14 @@ unittest
 
 private:
 
-enum cipherFunctionString = q{
+template isOnlyInputRange(R)
+{
+    enum isOnlyInputRange = isInputRange!R && !(isForwardRange!R);
+}
+
+enum cipherFunctionString(alias ReturnType, alias Constraint) = q{
     %s!(ElementType!R) cipherFunction(R)(R range, ubyte[32] key, ubyte[8] nonce, Cipher cipher)
-        if (is(ElementType!R : ubyte) && %s)
+        if (is(ElementType!R : ubyte) && %s!R)
     {
         final switch (cipher)
         {
@@ -49,4 +51,4 @@ enum cipherFunctionString = q{
                 return range.chacha20Cipher(key, nonce).inputRangeObject;
         }
     }
-};
+}.format(__traits(identifier, ReturnType), __traits(identifier, Constraint));