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digitalmars.D.learn - Why won't mmutable ranges stack?

reply doubleagent <doubleagent03 gmail.com> writes:
Compare the following two programs which take a string of whitespace separated
binary and decode it's message eg echo "01001101 01100101 01110010 01110010
01111001 00100000 01000011 01101000 01110010 01101001 01110011 01110100
01101101 01100001 01110011 00100001 00100001 00100001" | ./main.d

http://ompldr.org/vNnE5eA
http://ompldr.org/vNnE5eQ

The former works while the latter fails.  It looks like there's some
manipulation of 'bytes' and 'list' when writefln forces evaluation.  My
question is should this happen?

Also, is there a more idiomatic way to do byte conversions?  Something in the
stdlib, perhaps?
Dec 26 2010
parent reply "Simen kjaeraas" <simen.kjaras gmail.com> writes:
doubleagent <doubleagent03 gmail.com> wrote:


 The former works while the latter fails.  It looks like there's some
 manipulation of 'bytes' and 'list' when writefln forces evaluation.  My
 question is should this happen?


void main() {
     immutable auto bytes = splitter(stdin.readln(), ' ');
     immutable auto list = map!(byteToChar)(bytes); // Here
     immutable auto msg = reduce!("a ~ b")("", list);
     writefln("%s", msg);
}

The problem is on the marked line here - map and other non-array ranges
don't deal well with being immutable or const. Remove the immutable part
 from list, and it works wondrously:

void main() {
     immutable bytes = splitter(stdin.readln(), ' ');
     auto list = map!(byteToChar)(bytes); // Here
     immutable msg = reduce!("a ~ b")("", list);
     writefln("%s", msg);
}

Also note that auto is unnecessary when another storage class is
specified (const,immutable).

There have been several asking for tail-const (i.e. const(int)[])
support for ranges other than arrays. I have even written an
implementation that to an extent works, but more language support would
be preferable.



 Also, is there a more idiomatic way to do byte conversions?  Something  
 in the stdlib, perhaps?


std.conv.parse[1] with a second parameter (radix) of 2 works for me:




import std.stdio, std.algorithm, std.conv;

immutable(char) byteToChar(string b) {
     return cast(char)parse!ubyte(b,2);
}

void main() {
     immutable bytes = splitter(stdin.readln(), ' ');
     auto list = map!(byteToChar)(bytes);
     immutable msg = reduce!("a ~ b")("", list);
     writefln("%s", msg);
}


[1]: http://www.digitalmars.com/d/2.0/phobos/std_conv.html#parse
-- 
Simen
Dec 26 2010
parent reply doubleagent <doubleagent03 gmail.com> writes:
== Quote from Simen kjaeraas (simen.kjaras gmail.com)'s article

 Also note that auto is unnecessary when another storage class is
 specified (const,immutable).


Ah, that's right!



 There have been several asking for tail-const (i.e. const(int)[])
 support for ranges other than arrays. I have even written an
 implementation that to an extent works, but more language support would
 be preferable.


That seems like a really important feature to have.  If I'm not mistaken there
are
certain functional data structures which would be impossible to implement
without
first working around this limitation.  Is there a discussion thread for this?



 std.conv.parse[1] with a second parameter (radix) of 2 works for me:


Thanks!
Dec 26 2010
parent "Simen kjaeraas" <simen.kjaras gmail.com> writes:
doubleagent <doubleagent03 gmail.com> wrote:


 There have been several asking for tail-const (i.e. const(int)[])
 support for ranges other than arrays. I have even written an
 implementation that to an extent works, but more language support would
 be preferable.


 That seems like a really important feature to have.  If I'm not mistaken  
 there are
 certain functional data structures which would be impossible to  
 implement without
 first working around this limitation.  Is there a discussion thread for  
 this?


There is one in digitalmars.D, called tail const. Most of it is about a
month old.
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=123380

There is also bug 5377:
http://d.puremagic.com/issues/show_bug.cgi?id=5377

-- 
Simen
Dec 26 2010