Allow memoizing Results

examples/result.rs

@@ -0,0 +1,16 @@
+use memoize::memoize;
+
+#[memoize]
+fn hello(arg: String, arg2: usize) -> std::io::Result<bool> {
+    println!("{} => {}", arg, arg2);
+    Ok(arg.len() % 2 == arg2)
+}
+
+fn main() {
+    // `hello` is only called once here.
+    assert!(hello("World2".to_string(), 0).unwrap());
+    assert!(hello("World2".to_string(), 0).unwrap());
+    // Sometimes one might need the original function.
+    assert!(memoized_original_hello("World2".to_string(), 0).unwrap());
+    memoized_flush_hello();
+}

inner/Cargo.toml

@@ -19,6 +19,9 @@ proc-macro2 = "1.0"
 quote = "1.0"
 syn = { version = "1.0", features = ["full"] }
 
+[dev-dependencies]
+test-case = "3.3.1"
+
 [features]
 default = []
 full = []

inner/src/lib.rs

@@ -1,6 +1,6 @@
 #![crate_type = "proc-macro"]
 #![allow(unused_imports)] // Spurious complaints about a required trait import.
-use syn::{self, parse, parse_macro_input, spanned::Spanned, Expr, ExprCall, ItemFn, Path};
+use syn::{self, parse, parse2, parse_macro_input, spanned::Spanned, AngleBracketedGenericArguments, Expr, ExprCall, ItemFn, Path, PathArguments, Type};
 
 use proc_macro::TokenStream;
 use quote::{self, ToTokens};
@@ -110,6 +110,40 @@ impl parse::Parse for CacheOptions {
     }
 }
 
+
+fn check_for_result_type(outer: proc_macro2::TokenStream) -> bool {
+    // Parse the input as a Rust type
+    let input_ty = parse2::<Type>(outer).expect("failed to parse outer type");
+
+    if let Type::Path(path) = input_ty {
+        return path.path.segments.last().expect("O length path?").ident == "Result";
+    }
+    false
+}
+
+fn try_unwrap_result_type(outer: proc_macro2::TokenStream) -> proc_macro2::TokenStream {
+    let original = outer.clone();
+    // Parse the input as a Rust type
+    let input_ty = parse2::<Type>(outer).expect("failed to parse outer type");
+
+    // Ensure it’s a path type (e.g., Result<T, E>)
+    if let Type::Path(path) = input_ty {
+        // Look at the last segment (e.g., "Result")
+        let last_segment = path.path.segments.last().expect("Expected a Result");
+
+        if last_segment.ident.to_string().contains("Result") {
+            if let PathArguments::AngleBracketed(AngleBracketedGenericArguments { args, .. }) = &last_segment.arguments
+            {
+                // The first generic argument of Result<T, E> is the Ok type
+                if let Some(syn::GenericArgument::Type(ok_type)) = args.first() {
+                    return ok_type.to_token_stream()
+                }
+            }
+        }
+    }
+    original
+}
+
 // This implementation of the storage backend does not depend on any more crates.
 #[cfg(not(feature = "full"))]
 mod store {
@@ -122,6 +156,7 @@ mod store {
         key_type: proc_macro2::TokenStream,
         value_type: proc_macro2::TokenStream,
     ) -> (proc_macro2::TokenStream, proc_macro2::TokenStream) {
+        let value_type = crate::try_unwrap_result_type(value_type);
         // This is the unbounded default.
         if let Some(hasher) = &_options.custom_hasher {
             return (
@@ -148,8 +183,11 @@ mod store {
 // This implementation of the storage backend also depends on the `lru` crate.
 #[cfg(feature = "full")]
 mod store {
-    use crate::CacheOptions;
+    use crate::{try_unwrap_result_type, CacheOptions};
     use proc_macro::TokenStream;
+    use quote::quote;
+    use syn::{parse2, AngleBracketedGenericArguments, PathArguments, Type, TypePath};
+
 
     /// Returns TokenStreams to be used in quote!{} for parametrizing the memoize store variable,
     /// and initializing it.
@@ -161,6 +199,8 @@ mod store {
         key_type: proc_macro2::TokenStream,
         value_type: proc_macro2::TokenStream,
     ) -> (proc_macro2::TokenStream, proc_macro2::TokenStream) {
+        let value_type = try_unwrap_result_type(value_type);
+
         let value_type = match options.time_to_live {
             None => quote::quote! {#value_type},
             Some(_) => quote::quote! {(std::time::Instant, #value_type)},
@@ -201,7 +241,6 @@ mod store {
             }
         }
     }
-
     /// Returns names of methods as TokenStreams to insert and get (respectively) elements from a
     /// store.
     pub(crate) fn cache_access_methods(
@@ -379,20 +418,40 @@ pub fn memoize(attr: TokenStream, item: TokenStream) -> TokenStream {
         ),
     };
 
+    let get_value = if check_for_result_type(return_type.clone()) {
+        quote::quote! {
+            let ATTR_MEMOIZE_RETURN__ = #memoized_id #forwarding_tuple?;
+        }
+    } else {
+        quote::quote! {
+            let ATTR_MEMOIZE_RETURN__ = #memoized_id #forwarding_tuple;
+        }
+    };
+
+    let return_value = if check_for_result_type(return_type.clone()) {
+        quote::quote! {
+            Ok(ATTR_MEMOIZE_RETURN__)
+        }
+    } else {
+        quote::quote! {
+            ATTR_MEMOIZE_RETURN__
+        }
+    };
+
     let memoizer = if options.shared_cache {
         quote::quote! {
             {
                 let mut ATTR_MEMOIZE_HM__ = #store_ident.lock().unwrap();
                 if let Some(ATTR_MEMOIZE_RETURN__) = #read_memo {
-                    return ATTR_MEMOIZE_RETURN__
+                    return #return_value;
                 }
             }
-            let ATTR_MEMOIZE_RETURN__ = #memoized_id #forwarding_tuple;
+            #get_value
 
             let mut ATTR_MEMOIZE_HM__ = #store_ident.lock().unwrap();
             #memoize
 
-            ATTR_MEMOIZE_RETURN__
+            #return_value
         }
     } else {
         quote::quote! {
@@ -401,17 +460,17 @@ pub fn memoize(attr: TokenStream, item: TokenStream) -> TokenStream {
                 #read_memo
             });
             if let Some(ATTR_MEMOIZE_RETURN__) = ATTR_MEMOIZE_RETURN__ {
-                return ATTR_MEMOIZE_RETURN__;
+                return #return_value;
             }
 
-            let ATTR_MEMOIZE_RETURN__ = #memoized_id #forwarding_tuple;
+            #get_value
 
             #store_ident.with(|ATTR_MEMOIZE_HM__| {
                 let mut ATTR_MEMOIZE_HM__ = ATTR_MEMOIZE_HM__.borrow_mut();
                 #memoize
             });
 
-            ATTR_MEMOIZE_RETURN__
+            #return_value
         }
     };
 
@@ -505,4 +564,47 @@ fn check_signature(
 }
 
 #[cfg(test)]
-mod tests {}
+mod tests {
+    use std::str::FromStr;
+    use test_case::test_case;
+    use proc_macro2::TokenStream;
+    use quote::quote;
+    use crate::{check_for_result_type, try_unwrap_result_type};
+
+    #[test_case("Result<bool>")]
+    #[test_case("anyhow::Result<bool>")]
+    #[test_case("std::io::Result<bool>")]
+    #[test_case("io::Result<bool>")]
+    fn test_check_for_result_type_success(typestr: &str) {
+        let input = TokenStream::from_str(typestr).unwrap();
+        assert_eq!(true, check_for_result_type(input));
+    }
+
+    #[test_case("Option<bool>")]
+    #[test_case("(bool, bool)")]
+    #[test_case("bool")]
+    fn test_check_for_result_type_fail(typestr: &str) {
+        let input = TokenStream::from_str(typestr).unwrap();
+        assert_eq!(false, check_for_result_type(input));
+    }
+
+    #[test_case("Result<bool>", "bool")]
+    #[test_case("anyhow::Result<u32>", "u32")]
+    #[test_case("std::io::Result<String>", "String")]
+    #[test_case("io::Result<(u32, u32)>", "(u32 , u32)")]
+    #[test_case("CustomResult<CustomStruct, Error>", "CustomStruct")]
+    fn test_try_unwrap_result_type_inner(input_type: &str, output_type: &str) {
+        let input = TokenStream::from_str(input_type).unwrap();
+        assert_eq!(output_type,
+                   try_unwrap_result_type(input).to_string());
+    }
+
+    #[test_case("Option < bool >")]
+    #[test_case("(bool , bool)")]
+    #[test_case("bool")]
+    fn test_try_unwrap_result_type_original(typestr: &str) {
+        let input = TokenStream::from_str(typestr).unwrap();
+        assert_eq!(typestr.replace(" ", ""),
+                   try_unwrap_result_type(input).to_string().replace(" ", ""));
+    }
+}