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digitalmars.D.learn - Voldemort Type Construction Error

reply =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
I've made progress at the helper findingSplitter at

https://github.com/nordlow/justd/blob/master/substitution.d#L122

I need this for implementing a new Phobos lazy `substitute()` (or 
replace).

I've done most logic (AFAICT in my head) but I can't make the 
call to Result() work as it fails as

substitution.d(187,18): Error: struct 
substitution.findingSplitter!("a == b", string, string, string, 
string).findingSplitter.Result cannot deduce function from 
argument types !()(string, string, string, string), candidates 
are:
substitution.d(126,12):        substitution.findingSplitter!("a 
== b", string, string, string, string).findingSplitter.Result()
substitution.d(194,32): Error: template instance 
substitution.findingSplitter!("a == b", string, string, string, 
string) error instantiating
substitution.d(196,12): Error: undefined identifier 'equal', did 
you mean alias 'Unqual'?
/home/per/Work/justd/traits_ex.d(64,13): Warning: statement is 
not reachable

What have I missed?
Jan 15 2016
next sibling parent reply Anon <anon anon.anon> writes:
On Friday, 15 January 2016 at 14:04:50 UTC, Nordlöw wrote:

 What have I missed?


In line 126, `static struct Result()` is a template. Either drop 
the parens there, or change the call on line 187 to 
`Result!()(haystack, needles)`.
Jan 15 2016
parent reply =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
On Friday, 15 January 2016 at 16:51:24 UTC, Anon wrote:

 On Friday, 15 January 2016 at 14:04:50 UTC, Nordlöw wrote:

 What have I missed?


 In line 126, `static struct Result()` is a template. Either 
 drop the parens there, or change the call on line 187 to 
 `Result!()(haystack, needles)`.


Ahh, annoying mistake.

Why is this allowed?

/Per
Jan 15 2016
parent reply Kapps <opantm2+spam gmail.com> writes:
On Friday, 15 January 2016 at 20:04:47 UTC, Nordlöw wrote:

 On Friday, 15 January 2016 at 16:51:24 UTC, Anon wrote:

 On Friday, 15 January 2016 at 14:04:50 UTC, Nordlöw wrote:

 What have I missed?


 In line 126, `static struct Result()` is a template. Either 
 drop the parens there, or change the call on line 187 to 
 `Result!()(haystack, needles)`.


 Ahh, annoying mistake.

 Why is this allowed?

 /Per


At least for functions, making them templates provides some 
benefits like inferring attributes. Not sure if it behaves the 
same way on structs by making all functions within it templates.
Jan 15 2016
parent Jonathan M Davis via Digitalmars-d-learn writes:
On Saturday, January 16, 2016 06:06:03 Kapps via Digitalmars-d-learn wrote:

 On Friday, 15 January 2016 at 20:04:47 UTC, Nordlöw wrote:

 On Friday, 15 January 2016 at 16:51:24 UTC, Anon wrote:

 On Friday, 15 January 2016 at 14:04:50 UTC, Nordlöw wrote:

 What have I missed?


 In line 126, `static struct Result()` is a template. Either
 drop the parens there, or change the call on line 187 to
 `Result!()(haystack, needles)`.


 Ahh, annoying mistake.

 Why is this allowed?

 /Per


 At least for functions, making them templates provides some
 benefits like inferring attributes. Not sure if it behaves the
 same way on structs by making all functions within it templates.


It does

    struct S()
    {
        void foo()
        {
        }
    }

    void main()  safe
    {
        S!() s;
        s.foo();
    }

but having to do S!() for that rather than S is so ugly that I can't imagine
anyone actually doing it, whereas it's actually useful for functions -
particularly when you want to overload a templated function with one that
takes no template arguments. You _can_ finally overload those with normal
functions, but the overload rules don't work quite the same such that I
would normally avoid overloading a templated function with a non-templated
one.

- Jonathan M Davis
Jan 16 2016
prev sibling parent Jonathan M Davis via Digitalmars-d-learn writes:
On Friday, January 15, 2016 14:04:50 Nordlöw via Digitalmars-d-learn wrote:

 I've made progress at the helper findingSplitter at

 https://github.com/nordlow/justd/blob/master/substitution.d#L122

 I need this for implementing a new Phobos lazy `substitute()` (or
 replace).

 I've done most logic (AFAICT in my head) but I can't make the
 call to Result() work as it fails as

 substitution.d(187,18): Error: struct
 substitution.findingSplitter!("a == b", string, string, string,
 string).findingSplitter.Result cannot deduce function from
 argument types !()(string, string, string, string), candidates
 are:
 substitution.d(126,12):        substitution.findingSplitter!("a
 == b", string, string, string, string).findingSplitter.Result()
 substitution.d(194,32): Error: template instance
 substitution.findingSplitter!("a == b", string, string, string,
 string) error instantiating
 substitution.d(196,12): Error: undefined identifier 'equal', did
 you mean alias 'Unqual'?
 /home/per/Work/justd/traits_ex.d(64,13): Warning: statement is
 not reachable

 What have I missed?


Well, the last error is caused by not import equal in that code (since the
imports that would import it are local imports elsewhere in the module).

As for the main error, you have parens on the declaration of Result.

    static struct Result()

I don't know why you put them there, since Result is already effectively
templated by being inside of a templated function, and having it requires
that Result than have !() as a template argument when you're constructing
it. So, I'd say that you should just remove the parens - or if you have a
good reason that I can't think of which makes it make sense to put the
parens on Result, then you'll need to use !() when constructing it.

In any case, having the parens there but not using !() when constructing the
Result is what gives you the error you're seeing. If you remove the parens,
you get something more like

substitution.d(159): Error: template instance hasSlicing!R template
'hasSlicing' is not defined
substitution.d(160): Error: template instance hasLength!R template 'hasLength'
is not defined
substitution.d(176): Error: static assert  "Handle R without slicing"
substitution.d(195):        instantiated from here: findingSplitter!("a == b",
string, string, string, string)

Adding the appropriate imports results in something along the lines of

substitution.d(177): Error: static assert  "Handle R without slicing"
substitution.d(196):        instantiated from here: findingSplitter!("a == b",
string, string, string, string)

Beyond that, I'd have to figure out exactly what you're up to, but it looks
like that static assert is probably there to indicate that code needs to be
added as opposed to there being another bug that needs fixing.

In any case, that should at least help you make progress.

- Jonathan M Davis
Jan 15 2016