8 Commits
v0.2.3 ... main

Author SHA1 Message Date
017080244a build: update version to 1.0.0 2025-09-02 14:08:16 +02:00
12b209ad49 docs: update code documentation 2025-09-02 14:06:37 +02:00
8cac0af5c0 docs: simplify readme 2025-09-02 14:04:36 +02:00
nullstalgia
8a863f3b32 Copy conditional compilation flags onto created constructors (#13)
(Closes #12)
2025-09-02 13:43:29 +02:00
6c014e41a6 docs: update placement visibility (#11) 2025-04-22 14:26:00 +02:00
5fbcd2eb14 docs: remove code usage comment 2025-04-11 20:59:15 +02:00
baeb1969fe docs: add alternatives 2025-04-11 20:42:14 +02:00
0a12ee6b3f docs: add crates.io total downloads badge 2025-03-25 12:22:58 +01:00
5 changed files with 93 additions and 17 deletions

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@@ -1,6 +1,6 @@
[package]
name = "serde-inline-default"
version = "0.2.3"
version = "1.0.0"
authors = ["bytedream"]
edition = "2021"
description = "Serde default values via inline declaration"

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@@ -1,12 +1,12 @@
# serde-inline-default [![ci](https://github.com/ByteDream/serde-inline-default/actions/workflows/ci.yml/badge.svg)](https://github.com/ByteDream/serde-inline-default/actions/workflows/ci.yml) [![crates.io](https://img.shields.io/crates/v/serde-inline-default)](https://crates.io/crates/serde-inline-default) [![docs](https://img.shields.io/docsrs/serde-inline-default)](https://docs.rs/serde-inline-default/latest/serde_inline_default/)
# serde-inline-default [![ci](https://github.com/ByteDream/serde-inline-default/actions/workflows/ci.yml/badge.svg)](https://github.com/ByteDream/serde-inline-default/actions/workflows/ci.yml) [![crates.io](https://img.shields.io/crates/v/serde-inline-default)](https://crates.io/crates/serde-inline-default) [![crates.io downloads](https://img.shields.io/crates/d/serde-inline-default)](https://crates.io/crates/serde-inline-default) [![docs](https://img.shields.io/docsrs/serde-inline-default)](https://docs.rs/serde-inline-default/latest/serde_inline_default/)
Tiny crate to set default values for serde fields via inline attribute declaration.
A tiny crate to set default values for serde struct fields via inline attribute declaration.
## Overview
This crate is an approach to do what [serde-rs/serde#368](https://github.com/serde-rs/serde/issues/368) purposes.
If you want to set default values in plain [`serde`](https://serde.rs/), you have to create a function and link to it with `#[serde(default = "...")`.
This may be good if you need to do calculations to get the default value, but often you just want a simple integer or string to be the default value and have to create a whole function to return a hard-coded value.
This crate is an approach to do what [serde-rs/serde#368](https://github.com/serde-rs/serde/issues/368) purposes: Defining default values for struct fields via inline declaration instead of creating a separate function for it.
So instead of writing something like this, which can get very verbose quickly with many fields:
```rust
#[derive(Deserialize)]
struct Test {
@@ -16,11 +16,7 @@ struct Test {
fn value_default() -> u32 { 42 }
```
That can get quiet messy if you have many fields with many (different) default values.
This crate tries to solve this issue by providing the `#[serde_inline_default]` proc macro.
With this macro set at the struct level (_**before `#[derive(Deserialize)]`/`#[derive(Serialize)]`!, otherwise it's not working correctly**_), you can set default values via `#[serde_inline_default(...)]` for your serde fields inline, without creating an extra function.
you can just do this:
```rust
#[serde_inline_default]
#[derive(Deserialize)]
@@ -30,8 +26,53 @@ struct Test {
}
```
> [!IMPORTANT]
> **`#[serde_inline_default]` must be set before `#[derive(Deserialize)]`/`#[derive(Serialize)]`!**
Internally, `#[serde_inline_default(...)]` gets expanded to a function which returns the set value and the attribute is replaced with `#[serde(default = "<function name>")]`.
So this macro is just some syntax sugar for you, but can get quiet handy if you want to keep your code clean or write declarative macros / `macro_rules!`.
So this macro is just some syntax sugar for you, but can get quite handy if you want to keep your code clean or write declarative macros / `macro_rules!`.
## Alternatives
This crate isn't perfect. Thus, you might be more satisfied with alternatives `serde` provides.
With `#[serde(default)]` + `impl Default` on a struct, `serde` uses the default implementation of the struct to get default values for each field ([docs](https://serde.rs/container-attrs.html#default)):
```rust
#[derive(Deserialize)]
#[serde(default)]
struct Test {
value: u32
}
impl Default for Test {
fn default() -> Self {
Self {
value: 42
}
}
}
```
If you still need/want `serde-inline-default` features, you also can combine them with `#[serde(default))` and `impl Default`:
```rust
#[serde_inline_default]
#[derive(Deserialize)]
#[serde(default)]
struct Test {
value: u32,
#[serde_inline_default(0)]
other_value: u32,
}
impl Default for Test {
fn default() -> Self {
Self {
value: 42,
other_value: 42
}
}
}
```
## License

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@@ -14,16 +14,25 @@ pub(crate) fn expand_struct(mut item: ItemStruct) -> proc_macro::TokenStream {
let default: TokenStream = attr.parse_args().unwrap();
// copy all the same #[cfg] conditional compilations flags for the field onto our built
// default function.
// otherwise, it's possible to create a constructor for a type that may be filtered by
// the same #[cfg]'s, breaking compilation
let cfg_attrs = field.attrs.iter().filter(|a| a.path().is_ident("cfg"));
let fn_name_lit = format!("__serde_inline_default_{}_{}", item.ident, i);
let fn_name_ident = Ident::new(&fn_name_lit, Span::call_site());
let mut return_type = field.ty.clone();
// replaces most lifetimes with 'static
// replace lifetimes with 'static.
// the built default function / default values in general can only be static as they're
// generated without reference to the parent struct
type_lifetimes_to_static(&mut return_type);
inline_fns.push(quote! {
#[doc(hidden)]
#[allow(non_snake_case)]
#( #cfg_attrs )*
fn #fn_name_ident () -> #return_type {
#default
}

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@@ -8,12 +8,15 @@ mod utils;
/// The main macro of this crate.
/// Use it to define default values of fields in structs you [`Serialize`] or [`Deserialize`].
/// You do not need to create a extra function to provide the default value, as it is the case in serdes' implementation of default (`#[serde(default = "...")]`).
/// You do not need to create an extra function to provide the default value, as it is the case in
/// serdes' implementation of default (`#[serde(default = "...")]`).
///
/// Set this macro on a struct where you use [`Serialize`] or [`Deserialize`] and use `#[serde_inline_default(...)]` on the field you want to have a inline default value.
/// Replace the `...` with the value you want and it will be set as default if serde needs it.
/// Set this macro on a struct where you use [`Serialize`] or [`Deserialize`] and use
/// `#[serde_inline_default(...)]` on the field you want to have an inline default value.
/// Replace the `...` with the value you want, and it will be set as default if serde needs it.
///
/// Note that you must set this macro _before_ `#[derive(Serialize)]` / `#[derive(Deserialize)]` as it wouldn't work properly if set after the derive.
/// Note that you must set this macro _before_ `#[derive(Serialize)]` / `#[derive(Deserialize)]` as
/// it won't work properly if it's set after the derive.
///
/// # Examples
///

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@@ -43,3 +43,26 @@ fn test_lifetime() {
assert_eq!(lifetime_test.test_str, "test");
}
#[test]
#[allow(dead_code)]
fn test_conditional_compilation() {
#[cfg(debug_assertions)]
#[derive(Deserialize)]
struct TypeA(u8);
#[cfg(not(debug_assertions))]
#[derive(Deserialize)]
struct TypeB(u8);
#[serde_inline_default]
#[derive(Deserialize)]
struct Test {
#[cfg(debug_assertions)]
#[serde_inline_default(TypeA(1))]
val_a: TypeA,
#[cfg(not(debug_assertions))]
#[serde_inline_default(TypeB(1))]
val_b: TypeB,
}
}