&[Trait] should probably not be allowed

[Ms2ger]

This compiles:

trait Reader {}
fn perform(readers: &[Reader]) -> usize { 0 }

and this complains that there is no len():

trait Reader {}
fn perform(readers: &[Reader]) -> usize { readers.len() }

It seems to me like both should fail to compile with an error about sticking DSTs in a slice.

[steveklabnik]

/cc @rust-lang/lang , what do you think?

[nrc]

Yeah, we should require that T: Sized for [T], I think.

[nikomatsakis]

Note that you now get RFC 1214 warnings (i.e., this is largely fixed).

[nikomatsakis]

See e.g. http://is.gd/idE0a4

[steveklabnik]

Ahh yes, forgot about RFC 1214. Given that that will land, I think this is fine to close.