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Add syntax for negative implementations of traits

This commit introduces the syntax for negative implmenetations of traits
as shown below:

`impl !Trait for Type {}`

cc #13231
Part of RFC #3
This commit is contained in:
Flavio Percoco 2014-12-28 23:33:18 +01:00
parent 470118f3e9
commit 8b883ab268
34 changed files with 176 additions and 39 deletions

View file

@ -4802,6 +4802,13 @@ impl<'a> Parser<'a> {
// allow this to be parsed as a trait.
let could_be_trait = self.token != token::OpenDelim(token::Paren);
let neg_span = self.span;
let polarity = if self.eat(&token::Not) {
ast::ImplPolarity::Negative
} else {
ast::ImplPolarity::Positive
};
// Parse the trait.
let mut ty = self.parse_ty_sum();
@ -4824,6 +4831,14 @@ impl<'a> Parser<'a> {
ty = self.parse_ty_sum();
opt_trait_ref
} else {
match polarity {
ast::ImplPolarity::Negative => {
// This is a negated type implementation
// `impl !MyType {}`, which is not allowed.
self.span_err(neg_span, "inherent implementation can't be negated");
},
_ => {}
}
None
};
@ -4833,7 +4848,7 @@ impl<'a> Parser<'a> {
let ident = ast_util::impl_pretty_name(&opt_trait, &*ty);
(ident,
ItemImpl(unsafety, generics, opt_trait, ty, impl_items),
ItemImpl(unsafety, polarity, generics, opt_trait, ty, impl_items),
Some(attrs))
}