Summing with foldLeft

scala

Solution

The problem is that `a` is not a `Tuple`. If you annotate the function you pass to `foldLeft` you should see the problem:

val s1 = "1c0111001f010100061a024b53535009181c";
val s2 = "686974207468652062756c6c277320657965";
val zs : IndexedSeq[(Char, Char)] = s1.zip(s2);
val sum = zs.foldLeft(0)((a: Int , b: (Char, Char)) => a + (b._1 ^ b._2))

Remember that `a` is the accumulator and `b` is the current value. You want to accumulate `Int`s so `a` has to be of the same type as the seed you specify (`0`).

Of course you could write the above without the explicit annotations:

zs.foldLeft(0)((a, b) => a + (b._1 ^ b._2))

An even easier way would be to map it to an Int beforehand and then use the `sum` function:

val sum = s1.zip(s2)
  .map(cs => cs._1 ^ cs._2)
  .sum

Problem

In this code I'm attempting to sum the xor values of two Strings : ``` val s1 = "1c0111001f010100061a024b53535009181c"; val s2 = "686974207468652062756c6c277320657965"; val zs : IndexedSeq[(Char, Char)] = s1.zip(s2); zs.foldLeft(0)((a , b) => (a._1 ^ a._2) + (b._1 ^ b._2)) ``` I receive error message : ``` value _1 is not a member of Int [error] zs.foldLeft(0)((a , b) => (a._1 ^ a._2) + (b._1 ^ b._2)) [error] ^ [error] one error found [error] (test:compileIncremental) Compilation failed [error] Total time: 2 s, completed Oct 20, 2016 12:51:11 PM ``` As I'm folding over `(Char, Char)` should summing over xor of corresponding values be valid ?

Original source