blue-sky - 3 months ago 10

Scala Question

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)`

Answer

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
```