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Provides a Rust type and serialization/deserialization implementations for values that can be represented by 3 states: missing, present but null and present with a value.
```rust
pub enum Field
```
This can be useful when using JSON or other formats whereby the default in serde is to treat missing keys
and null values as the same, deserializing them to Option::None. A similar problem exists when serializing
as you have to create your own 3-state enum and tag each field with skip_serializing_if in order to not
serialize a field.
This can be problematic with APIs where partial objects or diffs are provided and you don't know whether you need to set the value to null or not update value should be left alone.
By using Field you are able to distinguish between null values and missing keys and get serde to
behave correctly in these scenarios.
```rust use serde::{Deserialize, Serialize}; use serdejson::json; use optionalfield::{Field, serdeoptionalfields};
struct Thing {
one: Field
fn main() {
let thing = serdejson::fromvalue::
assert_eq!(Field::Present(Some(1)), thing.one);
assert_eq!(Field::Present(None), thing.two);
assert_eq!(Field::Missing, thing.three);
} ```
Field implements many of the methods you are familiar with
on Option such as map, unwrap, as_ref etc. Field will return the value
from within the Option for these methods but also provides an equivalent set of methods for accessing the Option itself. These equivalent methods follow the
pattern of adding _present to the method name. For example, given Present(Some(100)), unwrap() will return 100 whereas unwrap_present() will return Some(100).
```rust use optional_field::Field;
struct Thing {
one: Field
fn main() { let numfield = Field::Present(Some(100)); // Calling map gets the value out of the Option within Present asserteq!(200, numfield.map(|n| n * 2)); // Calling mappresent gets the option out of Present asserteq!(false, numfield.mappresent(|opt| opt.isnone())); } ```
By default optional-field has serde and the serde macro as dependencies. If you
wish to use optional-field without pulling in serde you can set default-features to false.
toml
[dependencies]
optional-field = { version = "0.1.5", default-features = false }
MIT license (LICENSE.txt or http://opensource.org/licenses/MIT)