Hi there. I'm new to D language and make a simple software monitoring new file with specified extension.

class FileList
{
	str_CurrentDir;
	bool ReturnMatchedFile(string str_arg_filename, string str_Extension)
	{
	return endsWith(str_arg_filename, '.'~str_Extension);
	}

	void GetCurrentList(string str_arg_Extension)
	{
		auto filter_CurrentList=filter!ReturnMatchedFile(str_arg_Extension, dirEntries(str_CurrentDir, SpanMode.shallow));
	}
}

with this FileList class, after making instance of FileList and assigning str_CurrentDir variable, when I call GetCurrentList("d"), it says that std.algorithm.filter! ~~ does not match any function template declaration.
OK. So I modified above code like below just for a test.

class FileList
{
	str_CurrentDir;
	bool ReturnMatchedFile(string str_arg_filename)
	{
	return endsWith(str_arg_filename, ".d");
	}

	void GetCurrentList()
	{
		auto filter_CurrentList=filter!ReturnMatchedFile(dirEntries(str_CurrentDir, SpanMode.shallow));
	}
}

And it says that
this for ReturnMatchedFile needs to be type FileList not type FileResult!(ReturnMatchedFile, DirIterator).
I can't understand it!

Anyway, to solve the problem, again, I modified above code like below.

static bool ReturnMatchedFile(string str_arg_filename)
	{
	return endsWith(str_arg_filename, ".d");
	}

class FileList
{
	str_CurrentDir;
	
	void GetCurrentList()
	{
		auto filter_CurrentList=filter!ReturnMatchedFile(dirEntries(str_CurrentDir, SpanMode.shallow));
	}
}

and it works.

What is the problem?

Best regards and happy new year! :)

On 12/31/2012 08:11 AM, RollingCat wrote:
> Hi there. I'm new to D language and make a simple software monitoring
> new file with specified extension.
>
> class FileList
> {
> str_CurrentDir;
> bool ReturnMatchedFile(string str_arg_filename, string str_Extension)
> {
> return endsWith(str_arg_filename, '.'~str_Extension);
> }
>
> void GetCurrentList(string str_arg_Extension)
> {
> auto filter_CurrentList=filter!ReturnMatchedFile(str_arg_Extension,
> dirEntries(str_CurrentDir, SpanMode.shallow));
> }
> }
>
> with this FileList class, after making instance of FileList and
> assigning str_CurrentDir variable, when I call GetCurrentList("d"), it
> says that std.algorithm.filter! ~~ does not match any function template
> declaration.
> OK. So I modified above code like below just for a test.
>
> class FileList
> {
> str_CurrentDir;
> bool ReturnMatchedFile(string str_arg_filename)
> {
> return endsWith(str_arg_filename, ".d");
> }
>
> void GetCurrentList()
> {
> auto
> filter_CurrentList=filter!ReturnMatchedFile(dirEntries(str_CurrentDir,
> SpanMode.shallow));
> }
> }
>
> And it says that
> this for ReturnMatchedFile needs to be type FileList not type
> FileResult!(ReturnMatchedFile, DirIterator).
> I can't understand it!
>
> Anyway, to solve the problem, again, I modified above code like below.
>
> static bool ReturnMatchedFile(string str_arg_filename)
> {
> return endsWith(str_arg_filename, ".d");
> }
>
> class FileList
> {
> str_CurrentDir;
>
> void GetCurrentList()
> {
> auto
> filter_CurrentList=filter!ReturnMatchedFile(dirEntries(str_CurrentDir,
> SpanMode.shallow));
> }
> }
>
> and it works.
>
> What is the problem?
>
> Best regards and happy new year! :)

It is very helpful to see complete code. If I guessed it right, the following works:

import std.algorithm;
import std.file;

class FileList
{
    string str_CurrentDir;

    bool ReturnMatchedFile(string str_arg_filename, string str_Extension)
    {
        return endsWith(str_arg_filename, '.'~str_Extension);
    }

    void GetCurrentList(string str_arg_Extension)
    {
        auto filter_CurrentList =
            filter!(a => ReturnMatchedFile(a, str_arg_Extension))
                (dirEntries(str_CurrentDir, SpanMode.shallow));
    }
}

void main()
{
    auto f = new FileList();
}

The problem was that you did not provide the template argument parentheses to filter. You can omit them only if there is only one word.

I have used the lambda syntax as described here:

  http://dlang.org/expression.html#Lambda

Each element of dirEntries() appears to the lambda as its 'a' parameter. That parameter is then applied to the right-hand side of the => operator.

Unrelated to the question, I recommend that you don't use prefixes like 'str_' and 'arg_'; they make the code harder to read. For example, I would like 'desired_extension' better than 'str_arg_Extension', because it would carry its meaning better.

Also, predicates like ReturnMatchedFile() are usually named like hasMatchingExtension().

Ali

-- 
D Programming Language Tutorial: http://ddili.org/ders/d.en/index.html

Ali Çehreli:

> I would like 'desired_extension' better than 'str_arg_Extension', because it would carry its meaning better.

In D "desiredExtension'" is better than "desired_extension".

Bye,
bearophile

>> And it says that
>> this for ReturnMatchedFile needs to be type FileList not type
>> FileResult!(ReturnMatchedFile, DirIterator).
>> I can't understand it!
>>
>> Anyway, to solve the problem, again, I modified above code like below.
>>
>> static bool ReturnMatchedFile(string str_arg_filename)
>> {
>> return endsWith(str_arg_filename, ".d");
>> }
>>
>> class FileList
>> {
>> str_CurrentDir;
>>
>> void GetCurrentList()
>> {
>> auto
>> filter_CurrentList=filter!ReturnMatchedFile(dirEntries(str_CurrentDir,
>> SpanMode.shallow));
>> }
>> }
>>
>> and it works.
>>
>> What is the problem?
>>

Thanks for your reply. But what about the case of return type?

Regards.

On 01/01/2013 04:40 PM, RollingCat wrote:

> Thanks for your reply. But what about the case of return type?

I am sorry but I don't understand your question.

Even though you said "and it works" in your original post, the code does not compile. (For example, the line "str_CurrentDir;" looks like a member variable definition but it doesn't have a type!)

It looks like my guess at what you were trying to do has been wrong. It is very important that you show us what you are trying to do with a piece of real code.

Ali

Thank you very much.
Your answer helped me to solve the problem.

Regards