1 files changed, 68 insertions, 0 deletions
diff --git a/macros/src/fn_trait.rs b/macros/src/fn_trait.rs
new file mode 100644
index 0000000..f9b3514
--- /dev/null
+++ b/macros/src/fn_trait.rs
@@ -0,0 +1,68 @@
+use quote::ToTokens;
+use syn::parse::Parse;
+use syn::punctuated::Punctuated;
+use syn::token::Paren;
+use syn::{parenthesized, Ident, Token, 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,
+}
+
+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,
+        })
+    }
+}
+
+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);
+    }
+}