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August 16, 2010
readf for the novice
Since cstream is deprecated and stdio.readf is finally available with 
2.048, I started modifying my D book by replacing code like

    T var;
    din.readf(&var);

with

    T var;
    readf("%s", &var);


1) I couldn't go far, because stdio.readf does not ignore whitespace and 
code like the following fail:

    int i;
    int j;

    readf("%s", &i);
    readf("%s", &j);

When the input is

42 43

the output is

std.conv.ConvError: std.conv(1070): Can't convert value 
`LockingTextReader(File(807637C),  )' of type LockingTextReader to type int
[...]

Is that by design? Should the users strip the input themselves?


2) This is not a show stopper, but having to provide a format string for 
simple value input is unnecessary. It makes D less suitable for 
programming novices. (I see D very easy for novices in general, 
especially compared to C and C++.)


3) We need a simple way of reading values from stdin if only for the novice.

Another solution is using string.strip and conv.parse:

    auto line = strip(stdin.readln());
    auto i = parse!int(line);
    auto d = parse!double(line);

but that requires importing std.string and std.conv in addition to 
std.stdio. Also, with that, both of the values must be on the same line.

A novice should be able to read as simple as

    auto d = read!double();
    auto i = read!int();

Ignoring stripping whitespace, read can be implemented like this:

T read(T)()
{
    T value;
    readf("%s", &value);
    return value;
}

Actually stream.readf's signature was also nice. Can we do the same with 
stdio.readf?

  readf(&v0, &v1, &v2);

Ali
August 16, 2010
Re: readf for the novice
Ali Çehreli Wrote:

> Since cstream is deprecated and stdio.readf is finally available with 
> 2.048, I started modifying my D book by replacing code like
> 
>      T var;
>      din.readf(&var);
> 
> with
> 
>      T var;
>      readf("%s", &var);
> 
> 
> 1) I couldn't go far, because stdio.readf does not ignore whitespace and 
> code like the following fail:
> 
>      int i;
>      int j;
> 
>      readf("%s", &i);
>      readf("%s", &j);
> 
> When the input is
> 
> 42 43
> 
> the output is
> 
> std.conv.ConvError: std.conv(1070): Can't convert value 
> `LockingTextReader(File(807637C),  )' of type LockingTextReader to type int
> [...]
> 
> Is that by design? Should the users strip the input themselves?

It looks like a bug to me.

> 2) This is not a show stopper, but having to provide a format string for 
> simple value input is unnecessary. It makes D less suitable for 
> programming novices. (I see D very easy for novices in general, 
> especially compared to C and C++.)

Since D has TypeInfo for variadic arguments, you're right that a format string shouldn't often be necessary.

> 3) We need a simple way of reading values from stdin if only for the novice.
> 
> Another solution is using string.strip and conv.parse:
> 
>      auto line = strip(stdin.readln());
>      auto i = parse!int(line);
>      auto d = parse!double(line);
> 
> but that requires importing std.string and std.conv in addition to 
> std.stdio. Also, with that, both of the values must be on the same line.
> 
> A novice should be able to read as simple as
> 
>      auto d = read!double();
>      auto i = read!int();

Seems like a good idea to me.
August 16, 2010
Re: readf for the novice
Sean Kelly wrote:
> Ali Çehreli Wrote:
>>      int i;
>>      int j;
>>
>>      readf("%s", &i);
>>      readf("%s", &j);
>>
>> When the input is
>>
>> 42 43
>>
>> the output is
>>
>> std.conv.ConvError: std.conv(1070): Can't convert value
>> `LockingTextReader(File(807637C),  )' of type LockingTextReader to 
type int
>> [...]
>>
>> Is that by design? Should the users strip the input themselves?
>
> It looks like a bug to me.

Opened

  http://d.puremagic.com/issues/show_bug.cgi?id=4656

Thank you,
Ali
August 17, 2010
Re: readf for the novice
Ali Çehreli Wrote:

> A novice should be able to read as simple as
> 
>      auto d = read!double();
>      auto i = read!int();
> 
> Ignoring stripping whitespace, read can be implemented like this:
> 
> T read(T)()
> {
>      T value;
>      readf("%s", &value);
>      return value;
> }
> 
> Ali

I created a similar function for my own use. I used a question answer style:

auto age = userInput!int("Please Enter you age");

It is meant only to work with stdin and allows for some very nice extension functionality. For example Yes/No questions are possible:

if(userInput!bool("Do you want to continue?")) { ... }

I then added some other functions:

auto outputFolder = pathLocation("Where you do want to place the output?");
auto color = menu!string("What color would you like to use?", ["Blue", "Green"]);

Using pathLocation will verify that the folder/file exists before returning (maybe creating the path could be an option). And menu will display the array with numbers for selection; the input accepted is a integer or string and will return an integer or string depending on the request (default int).

If any of these seem common enough I'd be willing to clean them up and try to make them Range friendly.

I also have a function that takes a bool delegate which will continually ask for input and validates the answer against the delegate before returning.
August 17, 2010
Re: readf for the novice
Am 17.08.2010 19:10, schrieb Jesse Phillips:
> Ali �ehreli Wrote:
>
>> A novice should be able to read as simple as
>>
>>       auto d = read!double();
>>       auto i = read!int();
>>
>> Ignoring stripping whitespace, read can be implemented like this:
>>
>> T read(T)()
>> {
>>       T value;
>>       readf("%s",&value);
>>       return value;
>> }
>>
>> Ali
>
> I created a similar function for my own use. I used a question answer style:
>
> auto age = userInput!int("Please Enter you age");
>
> It is meant only to work with stdin and allows for some very nice extension functionality. For example Yes/No questions are possible:
>
> if(userInput!bool("Do you want to continue?")) { ... }
>
> I then added some other functions:
>
> auto outputFolder = pathLocation("Where you do want to place the output?");
> auto color = menu!string("What color would you like to use?", ["Blue", "Green"]);
>
> Using pathLocation will verify that the folder/file exists before returning (maybe creating the path could be an option). And menu will display the array with numbers for selection; the input accepted is a integer or string and will return an integer or string depending on the request (default int).
>
> If any of these seem common enough I'd be willing to clean them up and try to make them Range friendly.
>
> I also have a function that takes a bool delegate which will continually ask for input and validates the answer against the delegate before returning.
That sounds really cool. Having things like this in the std lib would 
allow you to write great consistent utilities with simple and short 
code. If such functions will ever get into phobos (what I really hope), 
they should get their own module. What do you thinke about 
'std.interact'? Anyways, sounds great!

Mafi
August 17, 2010
Re: readf for the novice
Mafi Wrote:

> That sounds really cool. Having things like this in the std lib would 
> allow you to write great consistent utilities with simple and short 
> code. If such functions will ever get into phobos (what I really hope), 
> they should get their own module. What do you thinke about 
> 'std.interact'? Anyways, sounds great!
> 
> Mafi

Is there anything you would consider adding? I guess I'll make the needed changes and submit it for review. I named the module cmdln.feedback  I never really thought that a great fit, but I can agree it really shouldn't be in std.stdio.
September 06, 2010
Re: readf for the novice
Those look really nice, they could especially be used in tutorials. I'm replicating some D1 examples from the dsource page to be D2 compatible, and I could add a bunch of more D2 examples as well. 

I'd be willing to write some tutorials for these if they get their way into Phobos.

Jesse Phillips Wrote:

> Mafi Wrote:
> 
> > That sounds really cool. Having things like this in the std lib would 
> > allow you to write great consistent utilities with simple and short 
> > code. If such functions will ever get into phobos (what I really hope), 
> > they should get their own module. What do you thinke about 
> > 'std.interact'? Anyways, sounds great!
> > 
> > Mafi
> 
> Is there anything you would consider adding? I guess I'll make the needed changes and submit it for review. I named the module cmdln.feedback  I never really thought that a great fit, but I can agree it really shouldn't be in std.stdio.
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