bool between(T, U1, U2)(T v, U1 lo, U2 hi)
{
    return v >= lo && v <= hi;
}

uint among(T, Us...)(T v, Us vals)
{
    foreach (i, U; Us)
    {
        if (v == vals[i]) return i + 1;
    }
    return 0;
}

Add?


Andrei

Andrei Alexandrescu:

> bool between(T, U1, U2)(T v, U1 lo, U2 hi)
> {
>     return v >= lo && v <= hi;
> }

I vote a +1 for between(). One use case:

http://rosettacode.org/wiki/Luhn_test_of_credit_card_numbers#Stronger_Statically_Typed_Version

It also helps in the D translation of Python expressions like:

if foo() and 3 < bar(x) < 5 and ...:

That in D need to be split in more lines unless bar() is pure and light.

-----------------

Regarding Phobos, currently one of the features I miss mostly is an optional template function for the min and max functions:

https://d.puremagic.com/issues/show_bug.cgi?id=4705#c16

Bye,
bearophile

On Monday, 16 December 2013 at 21:13:58 UTC, bearophile wrote:

> It also helps in the D translation of Python expressions like:
>
> if foo() and 3 < bar(x) < 5 and ...:

Not really, it uses "<=" which illustrates why it is better to use lambdas where a named function hides what goes on and there are several interpretations.

Besides, in many algos you want "low <= x < hi"  or the opposite to avoid double-hits on edge-cases.

On 12/16/2013 12:38 PM, Andrei Alexandrescu wrote:
> bool between(T, U1, U2)(T v, U1 lo, U2 hi)
> {
>      return v >= lo && v <= hi;
> }

You'd need 4 such functions, < <, < <=, <= <, <= <=, and it just seems like trivia.

>
> uint among(T, Us...)(T v, Us vals)
> {
>      foreach (i, U; Us)
>      {
>          if (v == vals[i]) return i + 1;
>      }
>      return 0;
> }

This has O(n) behavior, which might be unexpected for the user.

On Monday, 16 December 2013 at 20:38:52 UTC, Andrei Alexandrescu wrote:
> bool between(T, U1, U2)(T v, U1 lo, U2 hi)
> {
>     return v >= lo && v <= hi;
> }
>

I must say that:

    if (val.between(3, 10))

sure is a lot easier to understand at a glance than:

    if (val >= 3 && val <= 10)

Although there is a problem with the word "between" not being clear about whether it is inclusive or not.

I do kind of enjoy the Ruby-style DSL-lite they use to make code more readable so I'm for it.

On 12/16/2013 09:38 PM, Andrei Alexandrescu wrote:
> bool between(T, U1, U2)(T v, U1 lo, U2 hi)
> {
>      return v >= lo && v <= hi;
> }
> ...

There's the issue of different possibilities for inclusive/exclusive end points. Maybe we want to add a template parameter taking values from ["[)","()","(]","[]"]. Even then it is not too clear what the default should be. (Probably "[)".)

> uint among(T, Us...)(T v, Us vals)
> {
>      foreach (i, U; Us)
>      {
>          if (v == vals[i]) return i + 1;
>      }
>      return 0;
> }
> ...

I have my own version of this. I vote add.

On 12/16/2013 10:45 PM, Walter Bright wrote:
> On 12/16/2013 12:38 PM, Andrei Alexandrescu wrote:
>> bool between(T, U1, U2)(T v, U1 lo, U2 hi)
>> {
>>      return v >= lo && v <= hi;
>> }
>
> You'd need 4 such functions, < <, < <=, <= <, <= <=, and it just seems
> like trivia.
>
>>
>> uint among(T, Us...)(T v, Us vals)
>> {
>>      foreach (i, U; Us)
>>      {
>>          if (v == vals[i]) return i + 1;
>>      }
>>      return 0;
>> }
>
> This has O(n) behavior, which might be unexpected for the user.
>

Do you mean O(vals.length)? O(vals.length)=O(1).

On Monday, 16 December 2013 at 21:47:35 UTC, Brad Anderson wrote:
>     if (val >= 3 && val <= 10)

if (3 <= val && val <= 10)

Pretty clear.

On 12/16/2013 10:47 PM, Brad Anderson wrote:
> On Monday, 16 December 2013 at 20:38:52 UTC, Andrei Alexandrescu wrote:
>> bool between(T, U1, U2)(T v, U1 lo, U2 hi)
>> {
>>     return v >= lo && v <= hi;
>> }
>>
>
> I must say that:
>
>      if (val.between(3, 10))
>
> sure is a lot easier to understand at a glance than:
>
>      if (val >= 3 && val <= 10)
> ...

if (3 <= val && val <= 10)

is similarly easy to understand at a glance as the former. (Its drawback compared to that is that often a temporary variable will be required to be introduced in order to avoid recomputation.)

On 12/16/2013 1:47 PM, Brad Anderson wrote:
> On Monday, 16 December 2013 at 20:38:52 UTC, Andrei Alexandrescu wrote:
>> bool between(T, U1, U2)(T v, U1 lo, U2 hi)
>> {
>>     return v >= lo && v <= hi;
>> }
>>
>
> I must say that:
>
>      if (val.between(3, 10))
>
> sure is a lot easier to understand at a glance than:
>
>      if (val >= 3 && val <= 10)
>
> Although there is a problem with the word "between" not being clear about
> whether it is inclusive or not.

Exactly, meaning I'd have to go look at the source code for it, whereas with the latter I can see right away what it is. The function is a net programmer time loss.