The Insider News

Dave Kreskowiak wrote:

Damages for what??

Terrence Dorsey wrote:

never even seen a printed word?

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Or take string concatenation. If you pop open the implementation of string concatenation in Perl, Ruby, or JavaScript, you are certain to find an if statement, a realloc, and a memcpy. That is, when you concatenate two strings, the first string is grown to make room for the second, and then the second is copied into the first. This approach has worked for decades and is the “obvious” thing to do. Erlang's approach is non-obvious, and, I believe, correct. In the usual case, Erlang does not use a contiguous chunk of memory to represent a sequence of bytes. Instead, it something called an “I/O list” — a nested list of non-contiguous chunks of memory. The result is that concatenating two strings (I/O lists) takes O(1) time in Erlang, compared O(N) time in other languages. This is why template rendering in Ruby, Python, etc. is slow, but very fast in Erlang.

Judah Himango wrote:

a nested list of non-contiguous chunks of memory

Judah Himango wrote:

The result is that concatenating two strings (I/O lists) takes O(1) time in Erlang, compared O(N) time in other languages

AspDotNetDev wrote:

you'd have to scan through the linked list to find the one that contains the section of the string you are trying to substring, which turns an O(1) operation into an O(N) operation

string str = ...;
int lastIndex = 0;
int commaIndex;
while ((commaIndex = str.IndexOf(',', commaIndex)) != -1) {
    Process(substr, lastIndex, commaIndex);
    lastIndex = commaIndex + 1;
}

• The string passed to the Process method should be str, not substr;
• By passing commaIndex to the IndexOf function, this code would enter an infinite loop, if it would compile.
  (It actually generates a "use of unassigned local variable" compiler error.)
• If you change it to lastIndex, it will miss the last item in the string.