Re: Nice multiple dispatch details

For clarification: there are two concepts:

1) method declaration, for instance:
<T> String toString(!T);
and
String toString(Vehicle);

It has a return type, possible a contract, no code.

2) method implementation (or "method body" or "alternative"), for instance
toString(Car a) = "...";

It has no return type nor contract, but some code.

A method implementation belongs to one (or several, see below) method
declaration, for which it represents the code to execute in a certain
context.

A method declaration m2 can override another method declaration m1.
This happens when m2 is more specific than m1. It can in particular
have a more specific return type. In this case, all implementations of
m2 will also be implementations of m1.



On Feb 19, 2008 11:29 PM,  <[email protected]> wrote:
> There's one thing that I am a bit confused about.
>
> The code:
>         String toString(Vehicle a) = "a vehicle";
>         toString(Car a) = "a car";
>
> gives me this warning:
>
> ~/ca/corpus/nice/test1/main.nice: line 23, column 8:
> warning: This method overrides <T> java.lang.String toString(!T)
> You should make this explicit, either by omitting the return type
> or by using the 'override' keyword.
>
> What does 'overrides' mean here? If a method overrides another, does
> it imply that it is part of the same method (dispatch) group?
> So, in this case, is toString(test1.Vehicle a) part of toString(!T)?
> Is toString(Car a) part of toString(!T)?
>
> Additionally, the compiler seems to create a new method group
> toString(test1.Vehicle a) with the two alternatives:
>         toString(test1.Car a)
>         toString(test1.Vehicle a)
>
> >From this, it appears that a method body can be in multiple method
> groups. Is this correct?
>
> So for this call site:
>         toString(new Vehicle());
>
> the method group would be:
>         toString(test1.Car a)
>         toString(test1.Vehicle a)
>
>
> while for this call site:
>         toString(new java.lang.Object());
>
> the method group would be:
>         toString(!T)
>         toString(test1.Car a)
>         toString(test1.Vehicle a)
>
> Is this correct?

Yes, this is correct :-)

Daniel

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