Fixed stupid bug, so the different algos are actually used. However, we should find a better solution than using choose...

source/bitmanip.d

@@ -1,6 +1,7 @@
 module bitmanip;
 
 private import std.traits : isUnsigned;
+private import std.bitmanip : nativeToLittleEndian, littleEndianToNative;
 
 UIntType rotateLeft(UIntType)(in UIntType val, in size_t len) nothrow @nogc pure @safe
     if(isUnsigned!UIntType)
@@ -35,3 +36,26 @@ unittest
     assert(test[2].rotateRight(1) == 64);
     assert(test[2].rotateRight(7) == 1);
 }
+
+alias littleEndianInv = nativeToLittleEndian;
+
+uint littleEndian(in ubyte[] input) @safe pure nothrow @nogc
+in
+{
+    assert(input.length == uint.sizeof);
+}
+body
+{
+    ubyte[uint.sizeof] buf = input;
+    return littleEndianToNative!uint(buf);
+}
+
+unittest
+{
+    ubyte[] test0 = [0, 0, 0, 0];
+    ubyte[] test1 = [86, 75, 30, 9];
+    ubyte[] test2 = [255, 255, 255, 250];
+    assert(littleEndian(test0) == 0x00000000);
+    assert(littleEndian(test1) == 0x091e4b56);
+    assert(littleEndian(test2) == 0xfaffffff);
+}

source/chacha20.d

@@ -3,9 +3,9 @@ module chacha20;
 private import std.string : format;
 private import std.range : isInputRange, isForwardRange, ElementType;
 private import std.array;
+private import std.traits : hasElaborateCopyConstructor;
 
 private import bitmanip;
-private import endian;
 
 public:
 
@@ -67,6 +67,13 @@ auto chacha20Cipher(R)(R range, ubyte[32] key, ubyte[8] nonce)
                 return copy;
             }
         }
+
+        // We need this, so choose works with, if hasElaborateCopyConstructor!R
+        static if (hasElaborateCopyConstructor!R)
+        this(this)
+        {
+
+        }
     }
     return rangeResult(range, key, nonce);
 }

source/cipher.d

@@ -1,6 +1,6 @@
 module cipher;
 
-private import std.range : isInputRange, ElementType;
+private import std.range : isInputRange, ElementType, chooseAmong;
 private import salsa20;
 private import chacha20;
 import std.stdio;
@@ -16,12 +16,7 @@ enum Cipher
 auto cipherFunction(R)(R range, ubyte[32] key, ubyte[8] nonce, Cipher cipher)
     if(isInputRange!R && is(ElementType!R : ubyte))
 {
-    final switch(cipher)
-    {
-        case Cipher.salsa20:
-            return range.salsa20Cipher(key, nonce);
-
-        case Cipher.chacha20:
-            return range.salsa20Cipher(key, nonce);
-    }
+    return chooseAmong(cipher,
+                  range.salsa20Cipher(key, nonce),
+                  range.chacha20Cipher(key, nonce));
 }

source/endian.d

@@ -1,24 +1 @@
-private import std.bitmanip : nativeToLittleEndian, littleEndianToNative;
 
-alias littleEndianInv = nativeToLittleEndian;
-
-uint littleEndian(in ubyte[] input) @safe pure nothrow @nogc
-in
-{
-    assert(input.length == uint.sizeof);
-}
-body
-{
-    ubyte[uint.sizeof] buf = input;
-    return littleEndianToNative!uint(buf);
-}
-
-unittest
-{
-    ubyte[] test0 = [0, 0, 0, 0];
-    ubyte[] test1 = [86, 75, 30, 9];
-    ubyte[] test2 = [255, 255, 255, 250];
-    assert(littleEndian(test0) == 0x00000000);
-    assert(littleEndian(test1) == 0x091e4b56);
-    assert(littleEndian(test2) == 0xfaffffff);
-}

source/salsa20.d

@@ -3,9 +3,9 @@ module salsa20;
 private import std.string : format;
 private import std.range : isInputRange, isForwardRange, ElementType;
 private import std.array;
+private import std.traits : hasElaborateCopyConstructor;
 
 private import bitmanip;
-private import endian;
 
 public:
 
@@ -65,7 +65,16 @@ auto salsa20Cipher(R)(R range, ubyte[32] key, ubyte[8] nonce)
                 return copy;
             }
         }
+
+        // We need this, so choose works with, if hasElaborateCopyConstructor!R
+        static if (hasElaborateCopyConstructor!R)
+        this(this)
+        {
+
         }
+
+    }
+
     return rangeResult(range, key, nonce);
 }