Macro 3681
FYI
About this crate
MSRV
Since crate syn's msrv is 1.61, that also the msrv for this crate.
- Thinking about default values in structs.
- Implement via proc-macro.
- RFC-3681 default field values must be
const, which is not enough for most cases e.g. String.
Usage
cargo add macro3681
With Default derive
Default derive will be automatically removed, and generate an impl with default field values.
If there are none-default fields, those fields will be added as constructor parameters.
default_field_values! {
#[derive(Default, Debug)]
struct Example<'a, T, T2: Default> where T: Default {
i: u32 = 3,
j: i128,
i_option: Option<u64> = Some(1000),
string: String = {
let s = format!("{} {}", "hello", "world");
s
},
os: Option<String>,
foo: Foo = _, bytes: &'a[u8] = b"hello world",
t: T,
t2: T2,
}
}
Macro Expansion
#[derive(Debug)]
struct Example<'a, T, T2>
where
T: Default,
{
i: u32,
j: i128,
i_option: Option<u64>,
string: String,
os: Option<String>,
foo: Foo,
bytes: &'a [u8],
t: T,
t2: T2,
}
impl<'a, T, T2: Default> Example<'a, T, T2>
where
T: Default,
{
pub fn new(j: i128, os: Option<String>, t: T, t2: T2) -> Self {
Self {
i: 3,
j,
i_option: Some(1000),
string: {
let s = format!("{} {}", "hello", "world");
s
},
os,
foo: Default::default(),
bytes: b"hello world",
t,
t2,
}
}
}
impl<'a, T, T2: Default> Default for Example<'a, T, T2>
where
T: Default,
{
fn default() -> Self {
Self {
i: 3,
i_option: Some(1000),
string: {
let s = format!("{} {}", "hello", "world");
s
},
foo: Default::default(),
bytes: b"hello world",
j: Default::default(),
os: Default::default(),
t: Default::default(),
t2: Default::default(),
}
}
}
Without Default derive
Will not generate Self::default() function, only Self::new(..) is available
default_field_values! {
#[derive(Clone, Debug)]
pub(crate) struct Bar {
pub i: u32,
j: u32 = 100 * 4,
}
}
