Trait darling::FromMeta[−][src]

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.

`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>`[src]

`pub fn from_meta(item: &Meta) -> Result<Self, Error>`[src]

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>`[src]

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>`[src]

Create an instance from a list of nested meta items.

`pub fn from_value(value: &Lit) -> Result<Self, Error>`[src]

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>`[src]

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

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

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

`pub fn from_bool(value: bool) -> Result<Self, Error>`[src]

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

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Implementations on Foreign Types

`impl FromMeta for AtomicBool`[src]

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

`impl FromMeta for LitInt`[src]

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

`impl<T> FromMeta for Result<T, Error> where T: FromMeta,` [src]

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

`impl<T> FromMeta for Rc<T> where T: FromMeta,` [src]

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

`impl<T> FromMeta for RefCell<T> where T: FromMeta,` [src]

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

`impl FromMeta for i32`[src]

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

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

`impl FromMeta for Ident`[src]

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>`[src]

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

`impl FromMeta for WhereClause`[src]

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

`impl FromMeta for Path`[src]

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.