Re: logical operands on strings

[Ali Çehreli]

On 01/12/2014 10:21 AM, Erik van Velzen wrote:
I would like to do this:
     string one = x"315c4eeaa8b5f8aaf9174145bf43e1784b";
     string two = x"c29398f5f3251a0d47e503c66e935de81230b59b7a";
     string three = one ^ two;


The closests I've been able to get is:

     string three = xor(one, two);

     string xor(string one, string two) {
         int len = min(one.length, two.length);
         string result;
         for(int i=0; i<len; i++) {
             result ~= one[i] ^ two[i];
         }
         return cast(string)result;
     }

Question 1: is there a more elegant way to implement the function xor?
(foreach-ish or std.algorithm)


Then I tried to add operator overloading:

     string opBinary(string op)(string lhs, string rhs) {
         static if( op == "^" )
             return xor(lhs, rhs);
         else static assert(false, "operator not possible");
     }

But it doesn't invoke this function.

Question 2: how would I implement "^" for strings?

XOR is not a valid operation on a UTF-8 code unit. ;) It makes more 
sense to work with ubyte arrays. However, I found two usability issues 
with it:

1) std.conv.to did not work from string to ubyte[]; so, I wrote a function.

2) Array-wise operations does not support the following syntax

    auto three = one[] ^ two[];

Otherwise, ^= works with slices:

import std.stdio;

ubyte[] toBytes(string s)
{
    return cast(ubyte[])s.dup;
}

void main()
{
    ubyte[] one = x"55".toBytes;
    ubyte[] two = x"aa".toBytes;

    ubyte[] three = one.dup;
    three[] ^= two[];

    assert(one == x"55");
    assert(two == x"aa");
    assert(three == x"ff");
}

Ali