Hi All,
I have just recently discovered that it is possible to provide a trait
implementation for a reference type.
This feature by itself seems to me very controversial. But it also leads
to surprising dispatches when combined with argument matching for
references.
Consider following program:
trait A {
fn f(self);
fn g(&self);
}
impl A for int {
fn f(self) {
println!("f() for int");
}
fn g(&self) {
println!("g() for int");
}
}
impl<'a> A for &'a int {
fn f(self) {
println!("f() for reference");
}
fn g(&self) {
println!("g() for reference");
}
}
fn main() {
let one = 1i;
let one_ref = &one;
one_ref.f();
one_ref.g();
}
The output of this program is
f() for reference
g() for int
When I am analyzing this output, I can kinda understand how compiler finds
"the most suitable" implementation.
But this is still an example of a very tricky behavior we have so much of
in C++.
Is this a product of a conscious design decision or just a intermediate
state of the language which is under construction?
If it is by design, is there a place (RFC, github issue, mailing thread)
where I can read a discussion about pros and cons of allowing separate
trait implementations for references?
P.S.
If it matters my rust version is 0.12.0-pre-nightly (79a5448f4 2014-09-13
20:36:02 +0000)
Thanks,
Eugene Zemtsov.
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