Trait FromValue 

pub trait FromValue: Sized {
    // Required method
    fn from_value(v: Value) -> Result<Self, ShellError>;

    // Provided method
    fn expected_type() -> Type { ... }
}

A trait for loading a value from a Value.

Derivable

This trait can be used with #[derive].

When derived on structs with named fields, it expects a Value::Record where each field of the struct maps to a corresponding field in the record.

• If #[nu_value(rename = "...")] is applied to a field, that name will be used as the key in the record.
• If #[nu_value(rename_all = "...")] is applied on the container (struct) the key of the field will be case-converted accordingly.
• If neither attribute is applied, the field name is used as is.
• If #[nu_value(default)] is applied to a field, the field type’s Default implementation will be used if the corresponding record field is missing

Supported case conversions include those provided by heck, such as “snake_case”, “kebab-case”, “PascalCase”, and others. Additionally, all values accepted by #[serde(rename_all = "...")] are valid here.

For structs with unnamed fields, it expects a Value::List, and the fields are populated in the order they appear in the list. Unit structs expect a Value::Nothing, as they contain no data. Attempting to convert from a non-matching Value type will result in an error.

Only enums with no fields may derive this trait. The expected value representation will be the name of the variant as a Value::String.

• If #[nu_value(rename = "...")] is applied to a variant, that name will be used.
• If #[nu_value(rename_all = "...")] is applied on the enum container, the name of variant will be case-converted accordingly.
• If neither attribute is applied, the variant name will default to “snake_case”.

Additionally, you can use #[nu_value(type_name = "...")] in the derive macro to set a custom type name for FromValue::expected_type. This will result in a Type::Custom with the specified type name. This can be useful in situations where the default type name is not desired.

Enum Example

#[derive(FromValue, Debug, PartialEq)]
#[nu_value(rename_all = "COBOL-CASE", type_name = "birb")]
enum Bird {
    MountainEagle,
    ForestOwl,
    #[nu_value(rename = "RIVER-QUACK")]
    RiverDuck,
}

assert_eq!(
    Bird::from_value(Value::string("FOREST-OWL", span)).unwrap(),
    Bird::ForestOwl
);

assert_eq!(
    Bird::from_value(Value::string("RIVER-QUACK", span)).unwrap(),
    Bird::RiverDuck
);

assert_eq!(
    &Bird::expected_type().to_string(),
    "birb"
);

Struct Example

#[derive(FromValue, PartialEq, Eq, Debug)]
#[nu_value(rename_all = "kebab-case")]
struct Person {
    first_name: String,
    last_name: String,
    #[nu_value(rename = "age")]
    age_years: u32,
}

let value = Value::record(record! {
    "first-name" => Value::string("John", span),
    "last-name" => Value::string("Doe", span),
    "age" => Value::int(42, span),
}, span);

assert_eq!(
    Person::from_value(value).unwrap(),
    Person {
        first_name: "John".into(),
        last_name: "Doe".into(),
        age_years: 42,
    }
);

Required Methods

fn from_value(v: Value) -> Result<Self, ShellError>

Loads a value from a Value.

This method retrieves a value similarly to how strings are parsed using FromStr. The operation might fail if the Value contains unexpected types or structures.

Provided Methods

fn expected_type() -> Type

Expected Value type.

This is used to print out errors of what type of value is expected for conversion. Even if not used in from_value this should still be implemented so that other implementations like Option or Vec can make use of it. It is advised to call this method in from_value to ensure that expected type in the error is consistent.

Unlike the default implementation, derived implementations explicitly reveal the concrete type, such as Type::Record or Type::List, instead of an opaque type.

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.

Implementations on Foreign Types

impl FromValue for bool

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for char

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for f32

fn from_value(v: Value) -> Result<Self, ShellError>

impl FromValue for f64

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for i8

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for i16

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for i32

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for i64

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for isize

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for u16

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for u32

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for u64

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for ()

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for usize

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for String

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for Vec<u8>

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for Duration

This implementation supports positive durations only.

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for PathBuf

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for Bytes

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for DateTime<FixedOffset>

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroI8

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroI16

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroI32

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroI64

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroIsize

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroU16

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroU32

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroU64

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl FromValue for NonZeroUsize

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<B> FromValue for Cow<'_, B>

where B: ?Sized + ToOwned, B::Owned: FromValue,

This blanket implementation permits the use of Cow<'_, B> (Cow<'_, str> etc) based on the FromValue implementation of B’s owned form (str => String).

It’s meant to make using the FromValue derive macro on types that contain Cow fields possible.

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0> FromValue for (T0,)

where T0: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1> FromValue for (T0, T1)

where T0: FromValue, T1: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2> FromValue for (T0, T1, T2)

where T0: FromValue, T1: FromValue, T2: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3> FromValue for (T0, T1, T2, T3)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4> FromValue for (T0, T1, T2, T3, T4)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4, T5> FromValue for (T0, T1, T2, T3, T4, T5)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue, T5: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4, T5, T6> FromValue for (T0, T1, T2, T3, T4, T5, T6)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue, T5: FromValue, T6: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4, T5, T6, T7> FromValue for (T0, T1, T2, T3, T4, T5, T6, T7)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue, T5: FromValue, T6: FromValue, T7: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4, T5, T6, T7, T8> FromValue for (T0, T1, T2, T3, T4, T5, T6, T7, T8)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue, T5: FromValue, T6: FromValue, T7: FromValue, T8: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9> FromValue for (T0, T1, T2, T3, T4, T5, T6, T7, T8, T9)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue, T5: FromValue, T6: FromValue, T7: FromValue, T8: FromValue, T9: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> FromValue for (T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue, T5: FromValue, T6: FromValue, T7: FromValue, T8: FromValue, T9: FromValue, T10: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11> FromValue for (T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11)

where T0: FromValue, T1: FromValue, T2: FromValue, T3: FromValue, T4: FromValue, T5: FromValue, T6: FromValue, T7: FromValue, T8: FromValue, T9: FromValue, T10: FromValue, T11: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T> FromValue for Option<T>

where T: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T> FromValue for Vec<T>

where T: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<T, const N: usize> FromValue for [T; N]

where T: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

impl<V> FromValue for HashMap<String, V>

where V: FromValue,

fn from_value(v: Value) -> Result<Self, ShellError>

fn expected_type() -> Type

Implementors

impl FromValue for UseAnsiColoring

impl FromValue for DeprecationType

impl FromValue for NuGlob

impl FromValue for Range

impl FromValue for ReportMode

impl FromValue for Value

impl FromValue for CellPath

impl FromValue for ParsedKeybinding

impl FromValue for ParsedMenu

impl FromValue for Closure

impl FromValue for CustomExample

impl FromValue for DeprecationEntry

impl FromValue for Filesize

impl FromValue for IntRange

impl FromValue for Record

impl<T> FromValue for Spanned<T>

where T: FromValue,