Struct amplify_syn::SingularAttr

pub struct SingularAttr {
    pub name: String,
    pub value: ArgValue,
}

Structure describing a procedural macro attribute with an optional value. The means that if one has something like #[name1], #[name2 = "value"], #[name3 = ::std::path::PathBuf)] than name1, name2 = "value", and name3 = ::std::path::PathBuf are three different attributes which can be parsed and represented by the SingularAttr structure.

NB: For #[attr(arg1, arg2 = value)] style of proc macros use ParametrizedAttr structure. If you need to support both use Attr enum.

Internally the structure is composed of the name and value fields, where name is always a syn::Ident (corresponding name1, name2, name3 from the sample above) and value is an optional literal Lit, with corresponding cases of None, Some(ArgValue::Literal(Lit::Str(LitStr))), and Some(ArgValue::Type(Type::Path(Path))).

Fields

name: String

Optional attribute argument path part; for instance in #[my(name = value)] or in #[name = value] this is a name part

value: ArgValue

Attribute argument value part; for instance in #[name = value] this is the value part

Implementations

impl SingularAttr

pub fn new(name: impl ToString) -> Self

Constructs named SingularAttr without value

pub fn with(name: impl ToString, attrs: &[Attribute]) -> Result<Self, Error>

Constructs SingularAttr from a vector of all syn-parsed attributes, selecting single attribute matching the provided name. If there are multiple instances of the same attribute, fails with Error::SingularAttrRequired

pub fn with_literal(name: impl ToString, lit: Lit) -> Self

Constructs named SingularAttr setting its value to the provided literal

pub fn with_type(name: impl ToString, ty: Type) -> Self

Constructs named SingularAttr setting its value to the provided rust type value

pub fn from_attribute(attr: &Attribute) -> Result<Self, Error>

Constructs SingularAttr from a given syn::Attribute by parsing its data. Accepts only attributes having form #[attr(name = value)] and errors for other attribute types with Error::ArgNameMustBeIdent and Error::SingularAttrRequired

pub fn literal_value(&self) -> Result<Lit, Error>

Returns literal value, if any, or fails with Error::ArgValueRequired. See ArgValue::literal_value for the details.

pub fn type_value(&self) -> Result<Type, Error>

Returns type value, if any, or fails with Error::ArgValueRequired. See ArgValue::literal_value for the details.

pub fn merge(&mut self, other: Self) -> Result<(), Error>

Merges data from the other into the self.

Errors

• Fails with Error::NamesDontMatch if the names of the self and the other do not match
• Fails with Error::MultipleSingularValues if both self and the other has a named argument with the same name but different values.

pub fn merged(self, other: Self) -> Result<Self, Error>

Does merging as in SingularAttr::merge, but unlike it consumes the self and returns a merged structure in case of the successful operation. Useful in operation chains.

pub fn enrich(&mut self, attr: &Attribute) -> Result<(), Error>

Enriches current attribute data by adding information from the provided syn::Attribute.

Errors

• Fails with Error::NamesDontMatch if the names of the self and the provided attribute do not match
• Fails with Error::MultipleSingularValues if both self and the provided attribute has a named argument with the same name but different values.

pub fn enriched(self, attr: &Attribute) -> Result<Self, Error>

Performs enrich operation as in SingularAttr::enrich, but unlike it consumes the self and returns an enriched structure in case of the successful operation. Useful in operation chains.

pub fn check(&mut self, req: ArgValueReq) -> Result<(), Error>

Checks that the structure meets provided value requirements (see ArgValueReq), generating Error if the requirements are not met.

pub fn checked(self, req: ArgValueReq) -> Result<Self, Error>

Performs check as in SingularAttr::check, but unlike it consumes the self and returns a itself in case of the successful operation. Useful in operation chains.

Trait Implementations

impl Clone for SingularAttr

fn clone(&self) -> SingularAttr

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SingularAttr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.