I am trying to create 2 types which contain integral values but should not be compatible with each other. std.typecons.Typedef seems perfect for this:

alias QuestionId = Typedef!(long, long.init, "QuestionId");
alias StudentId = Typedef!(long, long.init, "StudentId");

However I'm failing to use using std.conv.to:
QuestionId q = to!QuestionId("34"); <-- gives compile errors

(This is a reduced example, the actual use case is to use std.csv to read in a structure from file, which in turn calls to!xyz)

How can I get std.conv to understand std.typecons.Typedef? In general, is there a better solution to orthogonal types than Typedef?

Thanks,
Saurabh

On Monday, 11 January 2016 at 08:03:19 UTC, Saurabh Das wrote:
>
> How can I get std.conv to understand std.typecons.Typedef?

You can do something like this:

QuestionId q = to!(TypedefType!QuestionId)("43");

> In general, is there a better solution to orthogonal types than Typedef?

Typedef is a reasonably solution, for this in my opinion.

togrue

On Monday, 11 January 2016 at 12:01:30 UTC, Tobi G. wrote:
> On Monday, 11 January 2016 at 08:03:19 UTC, Saurabh Das wrote:
>>
>> How can I get std.conv to understand std.typecons.Typedef?
>
> You can do something like this:
>
> QuestionId q = to!(TypedefType!QuestionId)("43");
>
>> In general, is there a better solution to orthogonal types than Typedef?
>
> Typedef is a reasonably solution, for this in my opinion.
>
> togrue

Oh excellent. Yes that works for a standalone conversion.  Do you know how I can use this with std.csv?

import std.typecons;
alias QuestionId = Typedef!(long, long.init, "QuestionId");
alias StudentId = Typedef!(long, long.init, "StudentId");

struct MyStuff
{
    QuestionId q;
    StudentId s;
}

void main()
{
    import std.csv, std.stdio, std.algorithm, std.range;
    File("file.csv").byLine.joiner("\n").csvReader!(MyStuff)(null).array;
}

This doesn't work. But if MyStuff is defined as: struct MyStuff { int q, s; }, then it works.

Any ideas?

On Monday, 11 January 2016 at 12:15:55 UTC, Saurabh Das wrote:
>
> Any ideas?

Yes. Because Typedef is introducing new Types, which csvReader doesn't know what they are,
you'll need a little workaround and cast the values yourself.

import std.csv, std.stdio, std.algorithm, std.range;

enum csvTxt = "10, 20
30, 40
50, 50";

myStuff = csvTxt.csvReader!(Tuple!(long, long))
	.map!(a => MyStuff(cast(QuestionId)a[0], cast(StudentId) a[1]))
        .array;


The .map does nothing other as getting the information out of the Tuple 'a' and constructing a struct of the type MyStuff.

togrue

On Monday, 11 January 2016 at 12:59:05 UTC, Tobi G. wrote:
> On Monday, 11 January 2016 at 12:15:55 UTC, Saurabh Das wrote:
>>
>> Any ideas?
>
> Yes. Because Typedef is introducing new Types, which csvReader doesn't know what they are,
> you'll need a little workaround and cast the values yourself.
>
> import std.csv, std.stdio, std.algorithm, std.range;
>
> enum csvTxt = "10, 20
> 30, 40
> 50, 50";
>
> myStuff = csvTxt.csvReader!(Tuple!(long, long))
> 	.map!(a => MyStuff(cast(QuestionId)a[0], cast(StudentId) a[1]))
>         .array;
>
>
> The .map does nothing other as getting the information out of the Tuple 'a' and constructing a struct of the type MyStuff.
>
> togrue

Yes that does make sense. I could read in a POD struct and convert it to a typed one.

Though I was hoping for a more elegant solution... This'll have to do I guess.

Thanks!