velcro_core 0.5.4

Core dependencies used by the `velcro` crate. See `velcro` for documentation. It is not advised to depend on this crate directly; it is an internal dependency of `velcro` and may be subject to breaking changes.
Documentation 
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use crate::seq::SeqInput;
use crate::value::{Value, ValueExpr, ValueIterExpr, Verbatim};
use proc_macro2::{Ident, Span, TokenStream};
use quote::{quote, ToTokens};
use syn::parse::{self, Parse, ParseStream};

pub struct IterInput<V = Verbatim>(SeqInput<V>);

impl<V> Parse for IterInput<V>
where
    Value<V>: Parse,
{
    fn parse(input: ParseStream<'_>) -> parse::Result<Self> {
        Ok(IterInput(input.parse()?))
    }
}

impl<V> IterInput<V>
where
    ValueExpr<V>: ToTokens,
    ValueIterExpr<V>: ToTokens,
{
    pub fn into_output(self) -> TokenStream {
        let target = Ident::new("it", Span::call_site());
        let updates = self.0.values().map(|value| match value {
            Value::One(expr) => quote! {
                let #target = #target.chain(std::iter::once(#expr));
            },
            Value::Many(expr) => quote! {
                let #target = #target.chain(#expr);
            },
        });
        quote! {{
            let #target = ::std::iter::empty();
            #(#updates)*
            #target
        }}
    }
}