pub trait AttributeValue: AttributeBase {
const EXPECTED: &'static str = "expected `=` or `(`";
const PREFERRED_OPEN_DELIMITER: &'static str = " = ";
const PREFERRED_CLOSE_DELIMITER: &'static str = "";
// Required method
fn parse_value(
input: ParseStream<'_>,
) -> Result<SpannedValue<Self::Partial>>;
// Provided methods
fn parse_value_meta(
input: ParseStream<'_>,
) -> Result<SpannedValue<Self::Partial>> { ... }
fn parse_value_eq(
input: ParseStream<'_>,
) -> Result<SpannedValue<Self::Partial>> { ... }
}Expand description
Any values that can be parsed in an attribute input.
This is probably the trait you want to implement when you created a custom
type for field inside #[derive(FromAttr)], as it will provide
implementations for FromAttr, AttributeNamed and, if you implement
the marker trait PositionalValue, AttributePositional as well.
For named attributes by default it will support both <name> = <value> and
<function>(<like>), though this can be tweaked in the implementation.
Provided Associated Constants§
Sourceconst EXPECTED: &'static str = "expected `=` or `(`"
const EXPECTED: &'static str = "expected `=` or `(`"
Printed when not encountering a ( or = respectively while trying to
parse a AttributeNamed.
Sourceconst PREFERRED_OPEN_DELIMITER: &'static str = " = "
const PREFERRED_OPEN_DELIMITER: &'static str = " = "
What open delimiter to use when providing error messages.
For <name> = <value>, this is " = ", for <function>(<like>), it is
"(".
As named attributes can allow both <name> = <value> and
name(<value>), this might not be the only way this attribute can be
used.
Sourceconst PREFERRED_CLOSE_DELIMITER: &'static str = ""
const PREFERRED_CLOSE_DELIMITER: &'static str = ""
What close delimiter to use when providing error messages.
For <name> = <value>, this is "", for <function>(<like>), it is
")".
As named attributes can allow both <name> = <value> and
<name>(<value>), this might not be the only way this attribute can be
used.
Required Methods§
Sourcefn parse_value(input: ParseStream<'_>) -> Result<SpannedValue<Self::Partial>>
fn parse_value(input: ParseStream<'_>) -> Result<SpannedValue<Self::Partial>>
Parses the plain attribute value without leading = or enclosing
parenthesis.
Note: this input includes potentially a trailing , and following
arguments.
attribute = value, ...
^^^^^^^^^^For simple syntax this is the only function needed to implement, as the
default implementations for parse_value_meta
and parse_value_eq.
Provided Methods§
Sourcefn parse_value_meta(
input: ParseStream<'_>,
) -> Result<SpannedValue<Self::Partial>>
fn parse_value_meta( input: ParseStream<'_>, ) -> Result<SpannedValue<Self::Partial>>
Parses the attribute value when parentheses (() were peeked.
Note: this is the input with the parentheses, and potentially following arguments.
attribute(value), ...
^^^^^^^^^^^^In the default implementation this calls through to
parse_value after removing the parentheses.
Sourcefn parse_value_eq(input: ParseStream<'_>) -> Result<SpannedValue<Self::Partial>>
fn parse_value_eq(input: ParseStream<'_>) -> Result<SpannedValue<Self::Partial>>
Parses the attribute value when an equals (=) was peeked.
Note: this is the input with the equals, and potentially following arguments.
attribute = value, ...
^^^^^^^^^^^^In the default implementation this calls through to
parse_value after removing the =.
Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.