[mercury-users] unsafe_set_char

[James Cussens]

Consider the following from the documentation for the string.m library 
module:

   % string.unsafe_set_char(Char, Index, String0, String):
  ...
   % This version is constant time, whereas string.set_char_det
   % may be linear in the length of the string. Use with care!

But I can't see how it can be constant time when it involves a call to 
strcpy. I feel I must be missing something here. What's going on?

More generally, being able to destructively update strings would be 
useful, I think. I'm using Mercury to implemenent hidden Markov models 
(which spit out strings) and currently make millions of calls to 
string.unsafe_set_char, so if anyone has tips on quick (perhaps dirty) 
methods of generating strings that would be appreciated. (My initial 
experiments seem to show that using string is better than array(char), btw.)

James

-- 
James Cussens
York Centre for Complex Systems Analysis             jc at cs.york.ac.uk
Department of Biology (Area 17)               Tel  +44 (0)1904 328396
University of York                            Fax  +44 (0)1904 500159
PO Box 373, York YO10 5YW, UK            http://www.cs.york.ac.uk/~jc
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