Trait Expected

Expected represents an explanation of what data a Visitor was expecting to receive.

This is used as an argument to the invalid_type, invalid_value, and invalid_length methods of the Error trait to build error messages. The message should be a noun or noun phrase that completes the sentence "This Visitor expects to receive ...", for example the message could be "an integer between 0 and 64". The message should not be capitalized and should not end with a period.

Within the context of a Visitor implementation, the Visitor itself (&self) is an implementation of this trait.

# use serde::de::{self, Unexpected, Visitor};
# use std::fmt;
#
# struct Example;
#
# impl<'de> Visitor<'de> for Example {
#     type Value = ();
#
#     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
#         write!(formatter, "definitely not a boolean")
#     }
#
fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
where
    E: de::Error,
{
    Err(de::Error::invalid_type(Unexpected::Bool(v), &self))
}
# }

Outside of a Visitor, &"..." can be used.

# use serde::de::{self, Unexpected};
#
# fn example<E>() -> Result<(), E>
# where
#     E: de::Error,
# {
#     let v = true;
return Err(de::Error::invalid_type(
    Unexpected::Bool(v),
    &"a negative integer",
));
# }