Trait darling::FromMeta

pub trait FromMeta {
    fn from_nested_meta(item: &NestedMeta) -> Result<Self, Error> { ... }
    fn from_meta(item: &Meta) -> Result<Self, Error> { ... }
    fn from_word() -> Result<Self, Error> { ... }
    fn from_list(items: &[NestedMeta]) -> Result<Self, Error> { ... }
    fn from_value(value: &Lit) -> Result<Self, Error> { ... }
    fn from_char(value: char) -> Result<Self, Error> { ... }
    fn from_string(value: &str) -> Result<Self, Error> { ... }
    fn from_bool(value: bool) -> Result<Self, Error> { ... }
}

Create an instance from an item in an attribute declaration.

Implementing FromMeta

• Do not take a dependency on the ident of the passed-in meta item. The ident will be set by the field name of the containing struct.
• Implement only the from_* methods that you intend to support. The default implementations will return useful errors.

Provided Implementations

bool

• Word with no value specified - becomes true.
• As a boolean literal, e.g. foo = true.
• As a string literal, e.g. foo = "true".

String

• As a string literal, e.g. foo = "hello".
• As a raw string literal, e.g. foo = r#"hello "world""#.

Number

• As a string literal, e.g. foo = "-25".
• As an unquoted positive value, e.g. foo = 404. Negative numbers must be in quotation marks.

()

• Word with no value specified, e.g. foo. This is best used with Option. See darling::util::Flag for a more strongly-typed alternative.

Option

• Any format produces Some.

Result<T, darling::Error>

• Allows for fallible parsing; will populate the target field with the result of the parse attempt.

Provided methods

fn from_nested_meta(item: &NestedMeta) -> Result<Self, Error>

fn from_meta(item: &Meta) -> Result<Self, Error>

Create an instance from a syn::Meta by dispatching to the format-appropriate trait function. This generally should not be overridden by implementers.

Error Spans

If this method is overridden and can introduce errors that weren't passed up from other from_meta calls, the override must call with_span on the error using the item to make sure that the emitted diagnostic points to the correct location in source code.

fn from_word() -> Result<Self, Error>

Create an instance from the presence of the word in the attribute with no additional options specified.

fn from_list(items: &[NestedMeta]) -> Result<Self, Error>

Create an instance from a list of nested meta items.

fn from_value(value: &Lit) -> Result<Self, Error>

Create an instance from a literal value of either foo = "bar" or foo("bar"). This dispatches to the appropriate method based on the type of literal encountered, and generally should not be overridden by implementers.

Error Spans

If this method is overridden, the override must make sure to add value's span information to the returned error by calling with_span(value) on the Error instance.

fn from_char(value: char) -> Result<Self, Error>

Create an instance from a char literal in a value position.

fn from_string(value: &str) -> Result<Self, Error>

Create an instance from a string literal in a value position.

fn from_bool(value: bool) -> Result<Self, Error>

Create an instance from a bool literal in a value position.

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Implementations on Foreign Types

impl FromMeta for u16

fn from_string(s: &str) -> Result<u16, Error>

fn from_value(value: &Lit) -> Result<u16, Error>

impl FromMeta for i32

fn from_string(s: &str) -> Result<i32, Error>

fn from_value(value: &Lit) -> Result<i32, Error>

impl FromMeta for LitByteStr

fn from_value(value: &Lit) -> Result<LitByteStr, Error>

impl FromMeta for String

fn from_string(s: &str) -> Result<String, Error>

impl FromMeta for LitStr

fn from_value(value: &Lit) -> Result<LitStr, Error>

impl FromMeta for f64

fn from_string(s: &str) -> Result<f64, Error>

fn from_value(value: &Lit) -> Result<f64, Error>

impl FromMeta for RenameRule

fn from_string(value: &str) -> Result<RenameRule, Error>

impl FromMeta for Vec<WherePredicate>

fn from_string(value: &str) -> Result<Vec<WherePredicate>, Error>

impl FromMeta for LitByte

fn from_value(value: &Lit) -> Result<LitByte, Error>

impl FromMeta for isize

fn from_string(s: &str) -> Result<isize, Error>

fn from_value(value: &Lit) -> Result<isize, Error>

impl<T> FromMeta for Option<T> where
    T: FromMeta, 

fn from_meta(item: &Meta) -> Result<Option<T>, Error>

impl FromMeta for LitInt

fn from_value(value: &Lit) -> Result<LitInt, Error>

impl FromMeta for Literal

fn from_value(value: &Lit) -> Result<Literal, Error>

impl FromMeta for LitBool

fn from_value(value: &Lit) -> Result<LitBool, Error>

impl<T> FromMeta for Result<T, Error> where
    T: FromMeta, 

fn from_meta(item: &Meta) -> Result<Result<T, Error>, Error>

impl FromMeta for WhereClause

fn from_string(value: &str) -> Result<WhereClause, Error>

impl<T> FromMeta for Box<T> where
    T: FromMeta, 

fn from_meta(item: &Meta) -> Result<Box<T>, Error>

impl FromMeta for Path

Parsing support for paths. This attempts to preserve span information when available, but also supports parsing strings with the call site as the emitted span.

fn from_string(value: &str) -> Result<Path, Error>

fn from_value(value: &Lit) -> Result<Path, Error>

impl FromMeta for Meta

fn from_meta(value: &Meta) -> Result<Meta, Error>

impl FromMeta for u8

fn from_string(s: &str) -> Result<u8, Error>

fn from_value(value: &Lit) -> Result<u8, Error>

impl FromMeta for u32

fn from_string(s: &str) -> Result<u32, Error>

fn from_value(value: &Lit) -> Result<u32, Error>

impl FromMeta for ()

fn from_word() -> Result<(), Error>

impl FromMeta for usize

fn from_string(s: &str) -> Result<usize, Error>

fn from_value(value: &Lit) -> Result<usize, Error>

impl FromMeta for LitFloat

fn from_value(value: &Lit) -> Result<LitFloat, Error>

impl FromMeta for LitChar

fn from_value(value: &Lit) -> Result<LitChar, Error>

impl<T> FromMeta for Arc<T> where
    T: FromMeta, 

fn from_meta(item: &Meta) -> Result<Arc<T>, Error>

impl FromMeta for i16

fn from_string(s: &str) -> Result<i16, Error>

fn from_value(value: &Lit) -> Result<i16, Error>

impl<V, S> FromMeta for HashMap<String, V, S> where
    S: Default + BuildHasher,
    V: FromMeta, 

fn from_list(nested: &[NestedMeta]) -> Result<HashMap<String, V, S>, Error>

impl FromMeta for Ident

Parsing support for identifiers. This attempts to preserve span information when available, but also supports parsing strings with the call site as the emitted span.

fn from_string(value: &str) -> Result<Ident, Error>

fn from_value(value: &Lit) -> Result<Ident, Error>

impl FromMeta for Lit

fn from_value(value: &Lit) -> Result<Lit, Error>

impl<T> FromMeta for Result<T, Meta> where
    T: FromMeta, 

Parses the meta-item, and in case of error preserves a copy of the input for later analysis.

fn from_meta(item: &Meta) -> Result<Result<T, Meta>, Error>

impl FromMeta for i8

fn from_string(s: &str) -> Result<i8, Error>

fn from_value(value: &Lit) -> Result<i8, Error>

impl FromMeta for i64

fn from_string(s: &str) -> Result<i64, Error>

fn from_value(value: &Lit) -> Result<i64, Error>

impl FromMeta for AtomicBool

fn from_meta(mi: &Meta) -> Result<AtomicBool, Error>

impl FromMeta for f32

fn from_string(s: &str) -> Result<f32, Error>

fn from_value(value: &Lit) -> Result<f32, Error>

impl FromMeta for u64

fn from_string(s: &str) -> Result<u64, Error>

fn from_value(value: &Lit) -> Result<u64, Error>

impl FromMeta for bool

fn from_word() -> Result<bool, Error>

fn from_bool(value: bool) -> Result<bool, Error>

fn from_string(value: &str) -> Result<bool, Error>

impl<T> FromMeta for Rc<T> where
    T: FromMeta, 

fn from_meta(item: &Meta) -> Result<Rc<T>, Error>

impl<T> FromMeta for RefCell<T> where
    T: FromMeta, 

fn from_meta(item: &Meta) -> Result<RefCell<T>, Error>

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Implementors

impl FromMeta for Flag

fn from_meta(mi: &Meta) -> Result<Flag, Error>

impl FromMeta for IdentString

fn from_meta(item: &Meta) -> Result<IdentString, Error>

impl FromMeta for Ignored

fn from_meta(&Meta) -> Result<Ignored, Error>

impl FromMeta for PathList

fn from_list(v: &[NestedMeta]) -> Result<PathList, Error>

impl<T> FromMeta for Override<T> where
    T: FromMeta, 

Parses a Meta. A bare word will produce Override::Inherit, while any value will be forwarded to T::from_meta.

fn from_word() -> Result<Override<T>, Error>

fn from_list(items: &[NestedMeta]) -> Result<Override<T>, Error>

fn from_value(lit: &Lit) -> Result<Override<T>, Error>

impl<T> FromMeta for SpannedValue<T> where
    T: FromMeta, 

fn from_meta(value: &Meta) -> Result<SpannedValue<T>, Error>

impl<T> FromMeta for WithOriginal<T, Meta> where
    T: FromMeta, 

fn from_meta(value: &Meta) -> Result<WithOriginal<T, Meta>, Error>

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