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digitalmars.D.learn - Templated function as associative array property

reply biozic <dransic free.fr> writes:
This problem might have been raised before, but I can't why this doesn't 
compile (except the last line), while a non-template version of the same 
code works well. Is this a bug?

---
module test;

template Graph(T)
{
     alias T[][T] Graph;
}

void add_edge(T)(ref Graph!(T) graph, T source, T target)
{
     graph[source] ~= target;
}

void main()
{
     Graph!(string) graph;

     graph.add_edge("A", "B");           // Error
     graph.add_edge!(string)("A", "B");  // Error
     add_edge(graph, "A", "B");          // Error
     add_edge!(string)(graph, "A", "B"); // OK
}
---

DMD 2.040, Mac OS X

Thanks,
Nicolas
Mar 07 2010
parent reply bearophile <bearophileHUGS lycos.com> writes:
biozic:


 This problem might have been raised before, but I can't why this doesn't 
 compile (except the last line), while a non-template version of the same 
 code works well. Is this a bug?


I don't know why your code doesn't work, someone more expert than me can answer
you. Maybe it's a bug.
In the meantime this works:

template Graph(T) {
    alias T[][T] Graph;
}

void add_edge(G, T)(ref G graph, T source, T target) if (is(G == Graph!T)) {
    graph[source] ~= target; // this is a slow operation
}

void main() {
    Graph!(string) graph;
    graph.add_edge("A", "B");
}

Bye,
bearophile
Mar 07 2010
parent reply biozic <dransic free.fr> writes:
Le 08/03/10 01:27, bearophile a écrit :

 I don't know why your code doesn't work, someone more expert than me can
answer you. Maybe it's a bug.
 In the meantime this works:


Yes, it works, thanks! But I believe this is just a workaround hack.


 graph[source] ~= target; // this is a slow operation


Yes, it's not the smartest graph implementation for D anyway :)


Nicolas
Mar 08 2010
parent reply bearophile <bearophileHUGS lycos.com> writes:
biozic:

 Yes, it works, thanks! But I believe this is just a workaround hack.


It's a workaround but it's not a hack. If no one else answers you then you can
add a bug to bugzilla... (I am not sure it's a real bug).

Bye,
bearophile
Mar 08 2010
parent reply Nicolas <biozic free.fr> writes:
bearophile Wrote:

 biozic:

 Yes, it works, thanks! But I believe this is just a workaround hack.


 
 It's a workaround but it's not a hack. If no one else answers you then you can
add a bug to bugzilla... (I am not sure it's a real bug).


Yes, you're right.
I think the problem can eventually be reduced to the following simple things:
---
module test;

void foo(T)(T[] array) {}

template Type(T) { alias T Type; }
void bar(T)(Type!T t) {}

void main()
{
    int[] a = [1, 2, 3];
    foo(a); // OK
    foo!int(a); // OK
    a.foo(); // OK
    //a.foo!int(); // Error: foo(a) isn't a template
    
    int b = 1;
    bar!int(b); // OK
    bar(b); // Error (template deduction fails)
}
---

The first error looks like a bug.
The second one: I don't know if the template deduction engine is supposed to
resolve this.
Mar 08 2010
next sibling parent bearophile <bearophileHUGS lycos.com> writes:
Nicolas:

 The first error looks like a bug.


Or maybe it's a limit of the compiler, it can even be a desired limit of the
syntax. I don't like to write that.



 The second one: I don't know if the template deduction engine is supposed to
resolve this.<


I think the answer is positive.
So I suggest you to file two bugs (even if the first one is not a bug, it can
be useful to add a note to the D docs that explain this syntax is not allowed).

Bye,
bearophile
Mar 08 2010
prev sibling parent reply bearophile <bearophileHUGS lycos.com> writes:
Nicolas:

 The first error looks like a bug.
 The second one: I don't know if the template deduction engine is supposed to
resolve this.


For now I have added the second only:
http://d.puremagic.com/issues/show_bug.cgi?id=3904

Bye,
bearophile
Mar 08 2010
parent biozic <dransic free.fr> writes:
Le 09/03/10 00:28, bearophile a écrit :

 Nicolas:

 The first error looks like a bug.
 The second one: I don't know if the template deduction engine is supposed to
resolve this.


 For now I have added the second only:
 http://d.puremagic.com/issues/show_bug.cgi?id=3904


Thanks. I've filed the first one, just in case.
Bye,
Nicolas
Mar 09 2010