Le 10/07/2012 01:33, Patrick Walton a écrit :
On 7/9/12 2:44 PM, David Bruant wrote:
As far as I can tell, the visibility control issue is not taken care of.
What it means is that when a trait is composed of other traits, the
instances of these traits have every single method of all the traits.
This doesn't help in defining well-encapsulated objects since it may
leaks implementation details (of "low-level" trait functions)
I have to admit to not having considered this in the design. However,
I think it's probably solvable the way we solve it in max/min classes:
the individual methods on a trait can be marked module-private.
I'm not sure it works. Consider the following (I'm not very familiar
with Rust syntax, so I apologize in advance for mistakes I would make):
trait Dot{
fn drawDot(x:int, y:int) -> ()
}
trait Shapes < Dot{
fn drawLine(/*...*/){
// use drawDot
}
fn drawCircle(/*...*/){
// use drawDot
}
// ...
}
trait Character < Shapes {
fn drawCharacter(/*...*/){
// use basic shapes (and maybe dots) to draw a character
}
}
I wish that instanciating a character (for a given type) shows the
drawCharacter method, but not any of the low-level drawing methods. I
don't think it's possible to make Dot and Shape methods module private
since Character could be in a different module (maybe I'm wrong, in
which case, I'm interested in seeing an example). Character needs these
methods to be implemented, but doesn't wish these methods to be provided
in its interface.
Why having both classes and traits? Both are mechanisms to enable code
reuse.
I guess I should restate my question: In which case would I use traits
over classes or classes over traits?
David
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