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> *You are reading the documentation for derive_constructors version 1.0.0*
Allows to derive multiple constructor functions and implement the [From] and [TryFrom] traits
for a struct by giving simple information such as their field's names.
Also allows to derive [From] for enums.
## 1 The Derive macros for structs: From and TryFrom
> Ref: [derive_constructors_proc::From], [derive_constructors_proc::TryFrom]
These allow you to Derive the [From] and [TryFrom] traits where a tuple of the fields are passed
to the [From::from] or [TryFrom::try_from] function, for example
``` rust
#[derive(derive_constructors::From, PartialEq, Debug)]
struct CharacterInfo{
name: String,
age: u8,
#[no_from]
times_appeared: u8,
#[no_from(4)]
years_studied: u8
}
let character_using_from = CharacterInfo::from(("Jorge".to_string(), 23));
let expected_character = CharacterInfo { name: "Jorge".to_string(), age: 23, times_appeared: 0, years_studied: 4};
assert_eq!(character_using_from, expected_character);
```
## 2 The Attribute Macro for structs:
> Ref: [derive_constructors_proc::constructor]
Allows you to define a constructor function, inside the proc attribute you can customize the
implementation by giving this information following attributes (Note every attribute is
optional):
- named: Name of the function, constructor functions are usually named like
'with_*name of the fields*', as calling them are quite readable, like
```CharacterInfo::with_name_and_age("Jorge", 23)```.
Note: If this field isn't given,
instead of implementing a 'with_*' constructor function, it will implement the [From] or
[TryFrom] trait.
- pattern (values: [From, TryFrom], default: From):
- When using the From pattern, the function receives fields as parameters and returns this
struct with said values, this is what you'll be looking for most of the time.
- When using the TryFrom pattern, the functions receives types that implement
Into, Into..., returning a [Ok] with your struct if every field could
successfully be turned to your field, in case not, it will return [Err] with an enum telling
which field couldn't get initialized and the Error why it didn't, see examples below for this.
- fields (default: All fields not included in the '```defaults```' attribute): Name of the
fields you want to create your constructor for, for example: ```fields(age, name)``` could
result in a function like: ```fn new(age: u8, name: String) -> CharacterInfo```.
- defaults: Tells how to initialize fields not covered in the ```fields``` attribute, for
example ```defaults(years_studied(4))```.
If a field isn't either on the ```fields``` or
```defaults``` attributes, it would count as it was initialized through [Default::default], this
means, the ```times_appeared``` field that hasn't been covered will be init as 0 (since
u8::default() is 0).
- error_enum_named (Only for the TryFrom pattern): Specifies the name for the enum error that
it's returned the TryFrom function fails.
- error_enum_metadata (Only for the TryFrom pattern): Declares the metadata for the enum error
that it's returned the TryFrom function fails, you will most likely want to write
```error_enum_metadata(#[derive(Debug)])``` in there.
## 2.1 Example 1: Empty constructor
If you just apply the [constructor] attribute, it will just implement the [From] trait where it
will take a tuple formed out of all your fields, in this case,
```from(value: (String, u8)) -> CharacterInfo```.
``` rust
#[derive(Debug, PartialEq)]
#[derive_constructors::constructor]
struct CharacterInfo{
name: String,
age: u8,
}
let character_using_from = CharacterInfo::from(("Jorge".to_string(), 23));
let expected_character = CharacterInfo { name: "Jorge".to_string(), age: 23 };
assert_eq!(character_using_from, expected_character);
```
## 2.2 Example 2: A 'new' constructor using specific fields
The following example creates a function named ```new(name: String, age: u8) -> CharacterInfo```
.
Since ```years_studied``` is specified, it will be initialized as 4, and since
```times_appeared``` is not, it will be initialized as u8::default() (which is 0).
``` rust
#[derive(Debug, PartialEq)]
#[derive_constructors::constructor(named(new), fields(name, age), defaults(years_studied(4)))]
struct CharacterInfo{
name: String,
age: u8,
times_appeared: u8,
years_studied: u8
}
let character_using_from = CharacterInfo::new("Jorge".to_string(), 23);
let expected_character = CharacterInfo { name: "Jorge".to_string(), age: 23, times_appeared: 0, years_studied: 4};
assert_eq!(character_using_from, expected_character);
```
## 2.3 Example 3: A 'new' constructor with the TryFrom pattern
The following example creates a function named ```new(name: T where String: TryFrom, age: U
where String: TryFrom) -> Result```.
Since ```years_studied``` is specified, it will be initialized as 4, and since
```times_appeared``` is not, it will be initialized as u8::default() (which is 0).
In case of an error, it returns a variant of an enum named ```MyEnumError```, this enum is
specified to derive [Debug] and [PartialEq].
``` rust
let character_using_try_from = CharacterInfo::new("Jorge", 23_u16).unwrap();
let expected_character = CharacterInfo { name: "Jorge".to_string(), age: 23, times_appeared: 0, years_studied: 4};
assert_eq!(character_using_try_from, expected_character);
let produced_error = u8::try_from(23000_u16).unwrap_err();
let forced_error_using_try_from = CharacterInfo::new("Jorge", 23000_u16).unwrap_err();
let expected_error_on_try_from = MyEnumError::AgeError(produced_error);
assert_eq!(forced_error_using_try_from, expected_error_on_try_from);
#[derive(Debug, PartialEq)]
#[derive_constructors::constructor(
named(new),
fields(name, age),
defaults(years_studied(4)),
pattern(TryFrom),
error_enum_named(MyEnumError),
error_enum_metadata(#[derive(Debug, PartialEq)])
)]
struct CharacterInfo{
name: String,
age: u8,
times_appeared: u8,
years_studied: u8,
}
```
## 3 The Derive macro for enums: From
> Ref: [derive_constructors_proc::From]
This implement the From trait for each enum by creating a From::from function on each taking
every field as value, for example:
```rust
#[derive(derive_constructors::From, Debug, PartialEq)]
enum MyValue{
StaticString(&'static str),
Number(i32),
Boolean(bool),
}
let scattered_values = vec![MyValue::from("Age "), MyValue::from(23), MyValue::from(", over age "), MyValue::from(true)];
let specified = vec![MyValue::StaticString("Age "), MyValue::Number(23), MyValue::StaticString(", over age "), MyValue::Boolean(true)];
assert_eq!(scattered_values, specified);
```