On 7/16/2011 4:13 PM, Willy Martinez wrote:
== Quote from Johann MacDonagh (johann.macdonagh...@spam.gmail.com)'s article
However, for what you want, you can use std.algorithm.filter
OK. Followed your advice and this is what I've got so far:
import std.algorithm;
import std.file;
import std.stdio;
void main(string[] args) {
auto needle = boyerMooreFinder(args[1]);
foreach (string name; dirEntries(".", SpanMode.shallow)) {
if (name[$-3 .. $] == "txt") {
writeln(name);
string text = readText(name);
auto haystack = filter!("a>= '0'&& a<= '9'")(text);
auto result = find(haystack, needle);
writeln(result);
}
}
}
Passing the haystack filter to find() produces the following error:
..\..\src\phobos\std\algorithm.d(2912): Error: function std.
algorithm.BoyerMooreFinder!(result,string).BoyerMooreFinder.beFound (string
haystack) is not callable using argument types (Filter!(result,string))
..\..\src\phobos\std\algorithm.d(2912): Error: cannot implicitly convert
expression (haystack) of type Filter!(result,string) to string
..\..\src\phobos\std\algorithm.d(2912): Error: cannot implicitly convert
expression (needle.beFound((__error))) of type string to Filter!(result,string)
search_seq.d(12): Error: template instance
std.algorithm.find!(Filter!(result,string),result,string) error instantiating
What could be the problem?
Thanks
Oh, I didn't see you wanted to do a Boyer-Moore search in your original
post. Dmitry basically explained what's wrong.
filter is lazy. When you do auto x = filter!... it doesn't filter right
away. It filters as you iterate over the range (this makes it much more
efficient). This means you can't find the xth element of a filtered
range (well you could, but it's not in O(1) time, which is why a
filtered range doesn't expose indexing operators).
You'll want to use array() over the filtered range that filter returns.
This will iterate over the entire filtered range and pull out each
element into an array. An array can be randomly accessed, which
Boyer-Moore needs. See Dmitry's post in your other topic.
