Crate synstructure
source ·Expand description
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
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
#[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.gen_impl(quote! {
extern crate synstructure_test_traits;
gen impl synstructure_test_traits::WalkFields for @Self {
fn walk_fields(&self, walk: &mut FnMut(&synstructure_test_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 {
#[allow(non_upper_case_globals)]
const _DERIVE_synstructure_test_traits_WalkFields_FOR_A: () = {
extern crate synstructure_test_traits;
impl<T> synstructure_test_traits::WalkFields for A<T>
where T: synstructure_test_traits::WalkFields
{
fn walk_fields(&self, walk: &mut FnMut(&synstructure_test_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
pub trait Interest {
fn interesting(&self) -> bool;
}
impl Interest for i32 {
fn interesting(&self) -> bool { *self > 0 }
}
Custom Derive
#[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 || synstructure_test_traits::Interest::interesting(#bi)
});
s.gen_impl(quote! {
extern crate synstructure_test_traits;
gen impl synstructure_test_traits::Interest for @Self {
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 {
#[allow(non_upper_case_globals)]
const _DERIVE_synstructure_test_traits_Interest_FOR_A: () = {
extern crate synstructure_test_traits;
impl<T> synstructure_test_traits::Interest for A<T>
where T: synstructure_test_traits::Interest
{
fn interesting(&self) -> bool {
match *self {
A::B(ref __binding_0, ref __binding_1,) => {
false ||
synstructure_test_traits::Interest::interesting(__binding_0) ||
synstructure_test_traits::Interest::interesting(__binding_1)
}
A::C(ref __binding_0,) => {
false ||
synstructure_test_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.
Macros
The
decl_derive!
macro declares a custom derive wrapper. It will parse the
incoming TokenStream
into a synstructure::Structure
object, and pass it
into the inner function.Run a test on a custom derive. This macro expands both the original struct
and the expansion to ensure that they compile correctly, and confirms that
feeding the original struct into the named derive will produce the written
output.
Structs
Information about a specific binding. This contains both an
Ident
reference to the given field, and the syn &'a Field
descriptor for that
field.A wrapper around a
syn::DeriveInput
which provides utilities for creating
custom derive trait implementations.This type is similar to
syn
’s Variant
type, however each of the fields
are references rather than owned. When this is used as the AST for a real
variant, this struct simply borrows the fields of the syn::Variant
,
however this type may also be used as the sole variant for a struct.A wrapper around a
syn::DeriveInput
’s variant which provides utilities
for destructuring Variant
s with match
expressions.Enums
Functions
Dumps an unpretty version of a tokenstream. Takes any type which implements
Display
.