Macro 3681
FYI
About this crate
Thinking about default values in structs.
Implement via proc-macro.
This is just a toy. Do not use in production.
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(Debug, Default)]
pub struct Foo<'a, 'b>
{
i: i32 = 1,
string: String = {
let s = format!("{} {}", "hello", "world");
s
}
option_string: Option<String>,
bytes: &'a[u8] = b"hello world",
bytes2: &'b[u8] = b"hello world",
b: bool,
}
}
Macro Expansion
#[derive(Debug)]
pub struct Foo<'a, 'b> {
i: i32,
string: String,
option_string: Option<String>,
bytes: &'a [u8],
bytes2: &'b [u8],
b: bool,
}
impl<'a, 'b> Foo<'a, 'b> {
pub fn new(option_string: Option<String>, b: bool) -> Self {
Self {
i: 1,
string: {
let s = format!("{} {}", "hello", "world");
s
}
,
option_string,
bytes: b"hello world",
bytes2: b"hello world",
b,
}
}
}
impl<'a, 'b> Default for Foo<'a, 'b> {
fn default() -> Self {
Self {
i: 1,
string: {
let s = format!("{} {}", "hello", "world");
s
}
,
bytes: b"hello world",
bytes2: b"hello world",
option_string: Default::default(),
b: 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,
}
}
Limitation
Cannot work with Generics.
