A)
I'd like to simplify notation of template function declarations involving
only single-argument boolean template constraints as follows:

example:
A1: 'auto myfunction ( isSomeString a, isInputRange b) {...}'

would be rewritten by compiler as:
A2: 'auto myfunction(T0,T1) (T0 a, T1 b) if(isSomeString!T1 a &&
isInputRange!T b) {...}'

IMO, A1 is less verbose and clearer than A2.

Obviously, more complex template constraints would still require the full syntax, but I'd argue this case is the most common.


More generally, the compiler would rewrite:
'auto myfunction(Tj...) (modifier_i Ei ai,...) if(condition(Tj) ) {...}'
as:
'auto myfunction(Tj...,T'k...) (modifier_i E'i ai,...) if(condition(Tj) &&
Ek!T'k &...) {...}'
where, for each i, if Ei is the name (in current scope) of a template that
has a single argument and that returns a boolean, then introduce E'i as
type T'i, else E'i=Ei; and k ranges over the list of indexes i that
represent the former case.


B)
Secondly, ddoc doesn't generate template constraints or does so very
inconsistently :
in http://dlang.org/phobos/std_algorithm.html we have:
template map(fun...) if (fun.length >= 1);
but all other template constraints are omitted, eg:
void fill(Range, Value)(Range range, Value filler); // template constraint
omitted.
Using the notation proposed in A, wherever applicable, would make
documentation clear.

Timothee Cour:

> A)
> I'd like to simplify notation of template function declarations involving
> only single-argument boolean template constraints as follows:
>
> example:
> A1: 'auto myfunction ( isSomeString a, isInputRange b) {...}'
>
> would be rewritten by compiler as:
> A2: 'auto myfunction(T0,T1) (T0 a, T1 b) if(isSomeString!T1 a &&
> isInputRange!T b) {...}'
>
> IMO, A1 is less verbose and clearer than A2.
>
> Obviously, more complex template constraints would still require the full
> syntax, but I'd argue this case is the most common.

See:
http://forum.dlang.org/thread/xaganckgcdkfcmjamogh@forum.dlang.org


> B)
> Secondly, ddoc doesn't generate template constraints or does so very
> inconsistently :
> in http://dlang.org/phobos/std_algorithm.html we have:
> template map(fun...) if (fun.length >= 1);
> but all other template constraints are omitted, eg:
> void fill(Range, Value)(Range range, Value filler); // template constraint
> omitted.
> Using the notation proposed in A, wherever applicable, would make documentation clear.

That sounds like a bug report for bugzilla.

Bye,
bearophile

On Mon, Jun 10, 2013 at 2:19 AM, bearophile <bearophileHUGS@lycos.com>wrote:

> Timothee Cour:
>
>
>  A)
>> I'd like to simplify notation of template function declarations involving only single-argument boolean template constraints as follows:
>>
>> example:
>> A1: 'auto myfunction ( isSomeString a, isInputRange b) {...}'
>>
>> would be rewritten by compiler as:
>> A2: 'auto myfunction(T0,T1) (T0 a, T1 b) if(isSomeString!T1 a &&
>> isInputRange!T b) {...}'
>>
>> IMO, A1 is less verbose and clearer than A2.
>>
>> Obviously, more complex template constraints would still require the full syntax, but I'd argue this case is the most common.
>>
>
> See: http://forum.dlang.org/thread/**xaganckgcdkfcmjamogh@forum.**dlang.org<http://forum.dlang.org/thread/xaganckgcdkfcmjamogh@forum.dlang.org>


ah, great! So I guess it must indeed be a good idea!

from the link:
>  If you have two or more types, they must be the same (if you don't want
this, you have to use the normal longer syntax)

In what I suggest, the restriction is much weaker so it'd be more generally applicable: for example, 'auto myfunction ( isSomeString a, isInputRange b)' would work in what I suggest but not with the proposal in the link. I don't think it adds any confusion.

Should I draft a DIP?
I'd like to get more feedback before though.


I'll also reply on the above link (CppNow 2013) for your second proposal
from cppnow (i think variant does already that).



>
>  B)
>> Secondly, ddoc doesn't generate template constraints or does so very
>> inconsistently :
>> in http://dlang.org/phobos/std_**algorithm.html<http://dlang.org/phobos/std_algorithm.html>we have:
>> template map(fun...) if (fun.length >= 1);
>> but all other template constraints are omitted, eg:
>> void fill(Range, Value)(Range range, Value filler); // template constraint
>> omitted.
>> Using the notation proposed in A, wherever applicable, would make
>> documentation clear.
>>
>
> That sounds like a bug report for bugzilla.
>

just filed: http://d.puremagic.com/issues/show_bug.cgi?id=10325

Timothee Cour:

> ah, great! So I guess it must indeed be a good idea!

I don't know. It's a cute idea, but I think it doesn't add a lot of value. What are its advantages in D beside reducing a little the amount of code?


> In what I suggest, the restriction is much weaker so it'd be more generally
> applicable: for example, 'auto myfunction ( isSomeString a, isInputRange
> b)' would work in what I suggest but not with the proposal in the link. I
> don't think it adds any confusion.

"myfunction(isSomeString a, isInputRange b)" should work.

The restriction was different, about code like:
myfunction2(isInputRange a, isInputRange b)

And then trying to instantiate myfunction2 with two types (for a and b) that are both input ranges but are two different types.


> Should I draft a DIP?

Feel free, but be prepared to not see lot of people interested in it.


> I'd like to get more feedback before though.

Right. Andrei is expert on this topic.


> just filed: http://d.puremagic.com/issues/show_bug.cgi?id=10325

I have added a note. It's good to help as much as possible the person that will write the patch :-)

Bye,
bearophile