Trait otter_base::prelude::Index 1.0.0[−][src]
pub trait Index<Idx> where
Idx: ?Sized, { type Output: ?Sized; fn index(&self, index: Idx) -> &Self::Output; }
Expand description
Used for indexing operations (container[index]
) in immutable contexts.
container[index]
is actually syntactic sugar for *container.index(index)
,
but only when used as an immutable value. If a mutable value is requested,
IndexMut
is used instead. This allows nice things such as
let value = v[index]
if the type of value
implements Copy
.
Examples
The following example implements Index
on a read-only NucleotideCount
container, enabling individual counts to be retrieved with index syntax.
use std::ops::Index; enum Nucleotide { A, C, G, T, } struct NucleotideCount { a: usize, c: usize, g: usize, t: usize, } impl Index<Nucleotide> for NucleotideCount { type Output = usize; fn index(&self, nucleotide: Nucleotide) -> &Self::Output { match nucleotide { Nucleotide::A => &self.a, Nucleotide::C => &self.c, Nucleotide::G => &self.g, Nucleotide::T => &self.t, } } } let nucleotide_count = NucleotideCount {a: 14, c: 9, g: 10, t: 12}; assert_eq!(nucleotide_count[Nucleotide::A], 14); assert_eq!(nucleotide_count[Nucleotide::C], 9); assert_eq!(nucleotide_count[Nucleotide::G], 10); assert_eq!(nucleotide_count[Nucleotide::T], 12);
Associated Types
Required methods
Implementations on Foreign Types
type Output = <I as SliceIndex<str>>::Output
Index into a serde_json::Value
using the syntax value[0]
or
value["k"]
.
Returns Value::Null
if the type of self
does not match the type of
the index, for example if the index is a string and self
is an array
or a number. Also returns Value::Null
if the given key does not exist
in the map or the given index is not within the bounds of the array.
For retrieving deeply nested values, you should have a look at the
Value::pointer
method.
Examples
let data = json!({ "x": { "y": ["z", "zz"] } }); assert_eq!(data["x"]["y"], json!(["z", "zz"])); assert_eq!(data["x"]["y"][0], json!("z")); assert_eq!(data["a"], json!(null)); // returns null for undefined values assert_eq!(data["a"]["b"], json!(null)); // does not panic
Access an element of this map. Panics if the given key is not present in the map.
match *val { Value::String(ref s) => Some(s.as_str()), Value::Array(ref arr) => arr[0].as_str(), Value::Object(ref map) => map["type"].as_str(), _ => None, }