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# synstructure
[](https://crates.io/crates/synstructure)
[](https://docs.rs/synstructure)
[](https://travis-ci.org/mystor/synstructure)
[](https://blog.rust-lang.org/2018/12/06/Rust-1.31-and-rust-2018.html)
> NOTE: What follows is an exerpt from the module level documentation. For full
> details read the docs on [docs.rs](https://docs.rs/synstructure/)
This crate provides helper types for matching against enum variants, and
extracting bindings to each of the fields in the deriving Struct or Enum in
a generic way.
If you are writing a `#[derive]` which needs to perform some operation on
every field, then you have come to the right place!
# Example: `WalkFields`
### Trait Implementation
```rust
pub trait WalkFields: std::any::Any {
fn walk_fields(&self, walk: &mut FnMut(&WalkFields));
}
impl WalkFields for i32 {
fn walk_fields(&self, _walk: &mut FnMut(&WalkFields)) {}
}
```
### Custom Derive
```rust
#[macro_use]
extern crate synstructure;
#[macro_use]
extern crate quote;
extern crate proc_macro2;
fn walkfields_derive(s: synstructure::Structure) -> proc_macro2::TokenStream {
let body = s.each(|bi| quote!{
walk(#bi)
});
s.bound_impl(quote!(example_traits::WalkFields), quote!{
fn walk_fields(&self, walk: &mut FnMut(&example_traits::WalkFields)) {
match *self { #body }
}
})
}
decl_derive!([WalkFields] => walkfields_derive);
/*
* Test Case
*/
fn main() {
test_derive! {
walkfields_derive {
enum A<T> {
B(i32, T),
C(i32),
}
}
expands to {
const _: () = {
extern crate example_traits;
impl<T> example_traits::WalkFields for A<T>
where T: example_traits::WalkFields
{
fn walk_fields(&self, walk: &mut FnMut(&example_traits::WalkFields)) {
match *self {
A::B(ref __binding_0, ref __binding_1,) => {
{ walk(__binding_0) }
{ walk(__binding_1) }
}
A::C(ref __binding_0,) => {
{ walk(__binding_0) }
}
}
}
}
};
}
}
}
```
# Example: `Interest`
### Trait Implementation
```rust
pub trait Interest {
fn interesting(&self) -> bool;
}
impl Interest for i32 {
fn interesting(&self) -> bool { *self > 0 }
}
```
### Custom Derive
```rust
#[macro_use]
extern crate synstructure;
#[macro_use]
extern crate quote;
extern crate proc_macro2;
fn interest_derive(mut s: synstructure::Structure) -> proc_macro2::TokenStream {
let body = s.fold(false, |acc, bi| quote!{
#acc || example_traits::Interest::interesting(#bi)
});
s.bound_impl(quote!(example_traits::Interest), quote!{
fn interesting(&self) -> bool {
match *self {
#body
}
}
})
}
decl_derive!([Interest] => interest_derive);
/*
* Test Case
*/
fn main() {
test_derive!{
interest_derive {
enum A<T> {
B(i32, T),
C(i32),
}
}
expands to {
const _: () = {
extern crate example_traits;
impl<T> example_traits::Interest for A<T>
where T: example_traits::Interest
{
fn interesting(&self) -> bool {
match *self {
A::B(ref __binding_0, ref __binding_1,) => {
false ||
example_traits::Interest::interesting(__binding_0) ||
example_traits::Interest::interesting(__binding_1)
}
A::C(ref __binding_0,) => {
false ||
example_traits::Interest::interesting(__binding_0)
}
}
}
}
};
}
}
}
```
For more example usage, consider investigating the `abomonation_derive` crate,
which makes use of this crate, and is fairly simple.
|
