Trait darling::FromMeta

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

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

pub 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.

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

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

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

Create an instance from a list of nested meta items.

pub 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.

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

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

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

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

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

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

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

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

impl FromMeta for WhereClause

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

impl FromMeta for i16

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

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

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

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

impl FromMeta for ()

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

impl FromMeta for LitChar

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

impl FromMeta for f32

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

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

impl FromMeta for u32

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

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

impl FromMeta for u16

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

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

impl FromMeta for i8

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

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

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

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

impl FromMeta for LitFloat

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

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

impl FromMeta for Literal

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

impl FromMeta for i64

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

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

impl FromMeta for String

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

impl<T, P> FromMeta for Punctuated<T, P> where
    P: Parse,
    T: Parse, 

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

pub fn from_value(value: &Lit) -> Result<Punctuated<T, P>, Error>

impl FromMeta for LitInt

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

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

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

impl FromMeta for LitByte

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

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

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

impl FromMeta for LitStr

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

impl FromMeta for LitByteStr

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

impl FromMeta for f64

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

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

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

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

impl FromMeta for Vec<WherePredicate, Global>

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

impl FromMeta for Lit

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

impl FromMeta for AtomicBool

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

impl FromMeta for LitBool

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

impl FromMeta for bool

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

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

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

impl FromMeta for usize

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

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

impl FromMeta for Meta

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

impl FromMeta for RenameRule

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

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

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

impl FromMeta for u8

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

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

impl FromMeta for i32

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

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

impl FromMeta for u64

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

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

impl FromMeta for isize

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

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

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

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

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Implementors

impl FromMeta for Flag

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

impl FromMeta for IdentString

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

impl FromMeta for Ignored

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

impl FromMeta for PathList

pub 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.

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

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

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

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

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

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

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

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