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digitalmars.D.learn - Better Return Value for findSplit*()

reply "Per =?UTF-8?B?Tm9yZGzDtnci?= <per.nordlow gmail.com> writes:
After having written a lot of text pattern matching functions 
using Phobos' findSplit, findSplitBefore, findSplitAfter, and 
some more I've written myself I've come to the conclusion that I 
would like to enhance these functions to instead return a struct 
instead of tuples. This struct would typically look like

struct FindSplit(T)
{
     T[3] data;
     T first() { return data[0]; }
     T separator() { return data[1]; }
     T second() { return data[2]; }
     T opIndex(size_t i) return { return data[i]; }
     cast(T : bool)() { return !separator.empty; }
}

This would enable the following useful syntax:

     if (const split = line.findSplit(`-`))
     {
         // do something with split
     }

instead of current

     const split = line.findSplit(`-`)
     if (!split[1].empty)
     {
     }

which is a constantly reoccurring pattern in D code processing 
text.

The cons I can think of is that split[N] (N being a CT-constant) 
will occurr in run-time instead of compile-time and of course 
that people relying on that return-type of findSplit() being a 
tuple will cause code-breakage.

What do you guys think;

- Add extra template-param that returns struct instead and make 
the current behaviour deprecated?
- Will happen for D3? :)
- Will never happen?

Destroy!
May 16 2015
parent reply "Jakob Ovrum" <jakobovrum gmail.com> writes:
On Saturday, 16 May 2015 at 09:36:30 UTC, Per Nordlöw wrote:

 After having written a lot of text pattern matching functions 
 using Phobos' findSplit, findSplitBefore, findSplitAfter, and 
 some more I've written myself I've come to the conclusion that 
 I would like to enhance these functions to instead return a 
 struct instead of tuples. This struct would typically look like

 struct FindSplit(T)
 {
     T[3] data;
     T first() { return data[0]; }
     T separator() { return data[1]; }
     T second() { return data[2]; }
     T opIndex(size_t i) return { return data[i]; }
     cast(T : bool)() { return !separator.empty; }
 }

 This would enable the following useful syntax:

     if (const split = line.findSplit(`-`))
     {
         // do something with split
     }

 instead of current

     const split = line.findSplit(`-`)
     if (!split[1].empty)
     {
     }

 which is a constantly reoccurring pattern in D code processing 
 text.

 The cons I can think of is that split[N] (N being a 
 CT-constant) will occurr in run-time instead of compile-time 
 and of course that people relying on that return-type of 
 findSplit() being a tuple will cause code-breakage.

 What do you guys think;

 - Add extra template-param that returns struct instead and make 
 the current behaviour deprecated?
 - Will happen for D3? :)
 - Will never happen?

 Destroy!


It can be implemented in a backwards-compatible way as a subtype 
of a Tuple.

struct FindSplit(R)
{
     Tuple!(R, "pre", R, "separator", R, "post") asTuple;

     bool opCast(T : bool)()
     {
         return !asTuple.separator.empty;
     }

     alias asTuple this;
}

Tuple!(R, "pre", R, "separator", R, "post") is a subtype of 
Tuple!(R, R, R), which should be the current return type.
May 16 2015
parent reply "Per =?UTF-8?B?Tm9yZGzDtnci?= <per.nordlow gmail.com> writes:
On Saturday, 16 May 2015 at 09:56:22 UTC, Jakob Ovrum wrote:

 It can be implemented in a backwards-compatible way as a 
 subtype of a Tuple.

 struct FindSplit(R)
 {
     Tuple!(R, "pre", R, "separator", R, "post") asTuple;

     bool opCast(T : bool)()
     {
         return !asTuple.separator.empty;
     }

     alias asTuple this;
 }

 Tuple!(R, "pre", R, "separator", R, "post") is a subtype of 
 Tuple!(R, R, R), which should be the current return type.


Nice! Should I make a PR?
May 16 2015
parent reply "Jakob Ovrum" <jakobovrum gmail.com> writes:
On Saturday, 16 May 2015 at 10:28:11 UTC, Per Nordlöw wrote:

 Nice! Should I make a PR?


I think that would be very welcome.
May 16 2015
parent "Per =?UTF-8?B?Tm9yZGzDtnci?= <per.nordlow gmail.com> writes:
On Saturday, 16 May 2015 at 10:47:36 UTC, Jakob Ovrum wrote:

 Nice! Should I make a PR?


 I think that would be very welcome.


https://github.com/D-Programming-Language/phobos/pull/3288
May 16 2015