I'm trying to test using a "static if" statement if a tuple of strings contains a particular string. What's the easiest/best way to do this?

On 2013-05-05, 01:42, Diggory wrote:

> I'm trying to test using a "static if" statement if a tuple of strings contains a particular string. What's the easiest/best way to do this?

http://dlang.org/phobos/std_typetuple#.staticIndexOf

-- 
Simen

On Sunday, 5 May 2013 at 00:10:27 UTC, Simen Kjaeraas wrote:
> On 2013-05-05, 01:42, Diggory wrote:
>
>> I'm trying to test using a "static if" statement if a tuple of strings contains a particular string. What's the easiest/best way to do this?
>
> http://dlang.org/phobos/std_typetuple#.staticIndexOf

It's not a TypeTuple, it's a tuple of strings.

Diggory:

> It's not a TypeTuple, it's a tuple of strings.

Then one simple way to do it is to convert it into an array of strings, and then use canFind:

[mytuple[]].canFind(needle)

Bye,
bearophile

On Sunday, 5 May 2013 at 00:33:34 UTC, bearophile wrote:
> Diggory:
>
>> It's not a TypeTuple, it's a tuple of strings.
>
> Then one simple way to do it is to convert it into an array of strings, and then use canFind:
>
> [mytuple[]].canFind(needle)
>
> Bye,
> bearophile

OK, that makes sense but I'm not sure I understand that syntax.

The documentation seems too say that "[mytuple]" will make an array, or that "mytuple[]" will make a slice from a tuple (presumably with no arguments it will slice the entire tuple?), so how does "[mytuple[]]" work?

Diggory:

> The documentation seems too say that "[mytuple]" will make an array,

Nope. You have to extract the inherent typetuple first. And this is what the [] syntax does (tested):


import std.stdio, std.typecons, std.algorithm;
void main() {
    auto t = tuple("foo", "bar", "spam");
    assert([t[]].canFind("bar"));
}

Bye,
bearophile

On Sunday, 5 May 2013 at 01:44:19 UTC, bearophile wrote:
> Diggory:
>
>> The documentation seems too say that "[mytuple]" will make an array,
>
> Nope. You have to extract the inherent typetuple first. And this is what the [] syntax does (tested):
>
>
> import std.stdio, std.typecons, std.algorithm;
> void main() {
>     auto t = tuple("foo", "bar", "spam");
>     assert([t[]].canFind("bar"));
> }
>
> Bye,
> bearophile

Is the behaviour of the empty [] when applied to tuples documented anywhere?

The problem is that this doesn't work if the tuple is empty:
Error: template std.algorithm.canFind does not match any function template declaration.

And unfortunately in the situation I need it for an empty tuple is one of the most likely scenarios.

Diggory:

> Is the behaviour of the empty [] when applied to tuples documented anywhere?

I don't remember.


> The problem is that this doesn't work if the tuple is empty:
> Error: template std.algorithm.canFind does not match any function template declaration.
>
> And unfortunately in the situation I need it for an empty tuple is one of the most likely scenarios.

I see. Then a good idea is to create a little function, to solve this. It should contain a static if that tests for the empty tuple and returns false in that case, and otherwise uses the canFind.

Bye,
bearophile