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digitalmars.D.learn - Ranges tutorial

reply Willy Martinez <wmartinez thisisnotmyrealemail.com> writes:
I was wondering if there's a tutorial available on how to write simple ranges.
Something like what I'm trying to do: Skip whitespace from text read from a
file.

It's difficult to search for "d ranges tutorial" in Google.

Thanks
Jul 16 2011
parent reply Johann MacDonagh <johann.macdonagh.no spam.gmail.com> writes:
On 7/16/2011 3:25 PM, Willy Martinez wrote:
 I was wondering if there's a tutorial available on how to write simple ranges.
 Something like what I'm trying to do: Skip whitespace from text read from a
file.

 It's difficult to search for "d ranges tutorial" in Google.

 Thanks

I found the best place to learn about ranges was simply the std.range documentation http://www.d-programming-language.org/phobos/std_range.html For example, you can see what an input range is by looking at the isInputRange template. However, for what you want, you can use std.algorithm.filter
Jul 16 2011
parent reply Willy Martinez <wmartinez thisisnotmyrealemail.com> writes:
== Quote from Johann MacDonagh (johann.macdonagh.no 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
Jul 16 2011
parent Johann MacDonagh <johann.macdonagh.no spam.gmail.com> writes:
On 7/16/2011 4:13 PM, Willy Martinez wrote:
 == Quote from Johann MacDonagh (johann.macdonagh.no 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.
Jul 16 2011