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Add explanation for E0607

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This commit is contained in:
Esteban Küber 2018-01-21 18:20:18 -08:00
parent 4e68e2a41a
commit fdfb9a2963
1 changed files with 25 additions and 4 deletions
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29
src/librustc_typeck/check/cast.rs
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@ -281,10 +281,31 @@ impl<'a, 'gcx, 'tcx> CastCheck<'tcx> {
.emit();
}
CastError::SizedUnsizedCast => {
type_error_struct!(fcx.tcx.sess, self.span, self.expr_ty, E0607,
"cannot cast thin pointer `{}` to fat pointer `{}`",
self.expr_ty,
fcx.ty_to_string(self.cast_ty)).emit();
let mut err = type_error_struct!(
fcx.tcx.sess,
self.span,
self.expr_ty,
E0607,
"cannot cast thin pointer `{}` to fat pointer `{}`",
self.expr_ty,
fcx.ty_to_string(self.cast_ty)
);
if fcx.tcx.sess.opts.debugging_opts.explain {
err.note(
"Thin pointers are \"simple\" pointers: they are purely a reference to a \
memory address.\n\n\
Fat pointers are pointers referencing \"Dynamically Sized Types\" (also \
called DST). DST don't have a statically known size, therefore they can \
only exist behind some kind of pointers that contain additional \
information. Slices and trait objects are DSTs. In the case of slices, \
the additional information the fat pointer holds is their size.");
err.note("to fix this error, don't try to cast directly between thin and fat \
pointers");
err.help("for more information about casts, take a look at [The Book]\
(https://doc.rust-lang.org/book/first-edition/\
casting-between-types.html)");
}
err.emit();
}
CastError::UnknownCastPtrKind |
CastError::UnknownExprPtrKind => {