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use quote::ToTokens;
use syn::parse::Parse;
use syn::punctuated::Punctuated;
use syn::token::Paren;
use syn::{parenthesized, parse_str, Ident, Token, TraitBound, Type};
/// A function trait. `dyn Fn(u32) -> String`
#[derive(Debug, Clone)]
pub struct FnTrait
{
pub dyn_token: Token![dyn],
pub trait_ident: Ident,
pub paren_token: Paren,
pub inputs: Punctuated<Type, Token![,]>,
pub r_arrow_token: Token![->],
pub output: Type,
pub trait_bounds: Punctuated<TraitBound, Token![+]>,
}
impl FnTrait
{
pub fn add_trait_bound(&mut self, trait_bound: TraitBound)
{
self.trait_bounds.push(trait_bound);
}
}
impl Parse for FnTrait
{
fn parse(input: syn::parse::ParseStream) -> syn::Result<Self>
{
let dyn_token = input.parse::<Token![dyn]>()?;
let trait_ident = input.parse::<Ident>()?;
if trait_ident.to_string().as_str() != "Fn" {
return Err(syn::Error::new(trait_ident.span(), "Expected 'Fn'"));
}
let content;
let paren_token = parenthesized!(content in input);
let inputs = content.parse_terminated(Type::parse)?;
let r_arrow_token = input.parse::<Token![->]>()?;
let output = input.parse::<Type>()?;
Ok(Self {
dyn_token,
trait_ident,
paren_token,
inputs,
r_arrow_token,
output,
trait_bounds: Punctuated::new(),
})
}
}
impl ToTokens for FnTrait
{
fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream)
{
self.dyn_token.to_tokens(tokens);
self.trait_ident.to_tokens(tokens);
self.paren_token.surround(tokens, |tokens_inner| {
self.inputs.to_tokens(tokens_inner);
});
self.r_arrow_token.to_tokens(tokens);
self.output.to_tokens(tokens);
if !self.trait_bounds.is_empty() {
let plus: Token![+] = parse_str("+").unwrap();
plus.to_tokens(tokens);
self.trait_bounds.to_tokens(tokens);
}
}
}
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