Derives for scribe static cow str

enumscribe_derive/src/lib.rs

@@ -27,7 +27,7 @@ macro_rules! proc_try {
 }
 
 #[proc_macro_derive(ScribeString, attributes(enumscribe))]
-pub fn derive_enum_to_string(input: TokenStream) -> TokenStream {
+pub fn derive_scribe_string(input: TokenStream) -> TokenStream {
     let input: DeriveInput = syn::parse(input)
         .expect("failed to parse input");
 
@@ -42,8 +42,12 @@ pub fn derive_enum_to_string(input: TokenStream) -> TokenStream {
 
     for variant in parsed_enum.variants.iter() {
         match variant.match_variant(
-            |name| Ok(quote! { <_ as ::std::borrow::ToOwned>::to_owned(#name) }),
-            |field| Ok(quote! { <_ as ::std::convert::Into<::std::string::String>>::into(#field) }),
+            |name| Ok(quote! {
+                <_ as ::std::borrow::ToOwned>::to_owned(#name)
+            }),
+            |field| Ok(quote! {
+                <_ as ::std::convert::Into<::std::string::String>>::into(#field)
+            }),
         ) {
             Ok(Some((pattern, result))) => {
                 match_patterns.push(pattern);
@@ -75,7 +79,7 @@ pub fn derive_enum_to_string(input: TokenStream) -> TokenStream {
 }
 
 #[proc_macro_derive(TryScribeString, attributes(enumscribe))]
-pub fn derive_try_enum_to_string(input: TokenStream) -> TokenStream {
+pub fn derive_try_scribe_string(input: TokenStream) -> TokenStream {
     let input: DeriveInput = syn::parse(input)
         .expect("failed to parse input");
 
@@ -91,8 +95,16 @@ pub fn derive_try_enum_to_string(input: TokenStream) -> TokenStream {
 
     for variant in parsed_enum.variants.iter() {
         match variant.match_variant(
-            |name| Ok(quote! { ::std::option::Option::Some(<_ as ::std::borrow::ToOwned>::to_owned(#name)) }),
-            |field| Ok(quote! { ::std::option::Option::Some(<_ as ::std::convert::Into<::std::string::String>>::into(#field)) }),
+            |name| Ok(quote! {
+                ::std::option::Option::Some(
+                    <_ as ::std::borrow::ToOwned>::to_owned(#name)
+                )
+            }),
+            |field| Ok(quote! {
+                ::std::option::Option::Some(
+                    <_ as ::std::convert::Into<::std::string::String>>::into(#field)
+                )
+            }),
         ) {
             Ok(Some((pattern, result))) => {
                 match_patterns.push(pattern);
@@ -123,6 +135,119 @@ pub fn derive_try_enum_to_string(input: TokenStream) -> TokenStream {
     }).into()
 }
 
+#[proc_macro_derive(ScribeCowStr, attributes(enumscribe))]
+pub fn derive_scribe_cow_str(input: TokenStream) -> TokenStream {
+    let input: DeriveInput = syn::parse(input)
+        .expect("failed to parse input");
+
+    let enum_data = proc_try!(get_enum_data(&input));
+    let parsed_enum = proc_try!(enums::parse_enum(enum_data));
+
+    let enum_ident = &input.ident;
+    let enum_idents = iter::repeat(enum_ident);
+
+    let mut match_patterns = Vec::with_capacity(parsed_enum.variants.len());
+    let mut match_results = Vec::with_capacity(parsed_enum.variants.len());
+
+    for variant in parsed_enum.variants.iter() {
+        match variant.match_variant(
+            |name| Ok(quote! {
+                ::std::borrow::Cow::Borrowed(#name)
+            }),
+            |field| Ok(quote! {
+                ::std::borrow::Cow::Owned(
+                    <_ as ::std::convert::Into<::std::string::String>>::into(#field)
+                )
+            }),
+        ) {
+            Ok(Some((pattern, result))) => {
+                match_patterns.push(pattern);
+                match_results.push(result);
+            },
+
+            Ok(None) => return MacroError::new(format!(
+                "cannot derive ScribeCowStr for {} because the variant {} is marked as {}\n\
+                 explanation: since {} is ignored, it cannot be guaranteed that the enum can \
+                 always be successfully converted to a String\n\
+                 hint: try deriving TryScribeCowStr instead",
+                enum_ident.to_string(), variant.data.ident.to_string(), IGNORE,
+                variant.data.ident.to_string(),
+            ), variant.span).into(),
+
+            Err(err) => return err.into()
+        }
+    }
+
+    (quote! {
+        impl ::enumscribe::ScribeCowStr for #enum_ident {
+            fn scribe(&self) -> ::std::borrow::Cow<'static, str> {
+                match self {
+                    #(#enum_idents::#match_patterns => #match_results,)*
+                }
+            }
+        }
+    }).into()
+}
+
+#[proc_macro_derive(TryScribeCowStr, attributes(enumscribe))]
+pub fn derive_try_scribe_cow_str(input: TokenStream) -> TokenStream {
+    let input: DeriveInput = syn::parse(input)
+        .expect("failed to parse input");
+
+    let enum_data = proc_try!(get_enum_data(&input));
+    let parsed_enum = proc_try!(enums::parse_enum(enum_data));
+
+    let enum_ident = &input.ident;
+    let enum_idents = iter::repeat(enum_ident);
+
+    let mut ignore_variant = false;
+    let mut match_patterns = Vec::with_capacity(parsed_enum.variants.len());
+    let mut match_results = Vec::with_capacity(parsed_enum.variants.len());
+
+    for variant in parsed_enum.variants.iter() {
+        match variant.match_variant(
+            |name| Ok(quote! {
+                ::std::option::Option::Some(
+                    ::std::borrow::Cow::Borrowed(#name)
+                )
+            }),
+            |field| Ok(quote! {
+                ::std::option::Option::Some(
+                    ::std::borrow::Cow::Owned(
+                        <_ as ::std::convert::Into<::std::string::String>>::into(#field)
+                    )
+                )
+            }),
+        ) {
+            Ok(Some((pattern, result))) => {
+                match_patterns.push(pattern);
+                match_results.push(result);
+            },
+
+            Ok(None) => ignore_variant = true,
+
+            Err(err) => return err.into()
+        }
+    }
+
+    let ignore_arm = if ignore_variant {
+        quote! { _ => ::std::option::Option::None, }
+    } else {
+        quote! {}
+    };
+
+    (quote! {
+        impl ::enumscribe::TryScribeCowStr for #enum_ident {
+            fn try_scribe(&self) -> ::std::option::Option<::std::borrow::Cow<'static, str>> {
+                match self {
+                    #(#enum_idents::#match_patterns => #match_results,)*
+                    #ignore_arm
+                }
+            }
+        }
+    }).into()
+}
+
 fn get_enum_data(input: &DeriveInput) -> MacroResult<&DataEnum> {
     let enum_data = match &input.data {
         Data::Enum(enum_data) => enum_data,

enumscribe_examples/examples/airports.rs

@@ -1,7 +1,8 @@
 use enumscribe::*;
 
 // #[derive(ScribeString)]
-#[derive(TryScribeString)]
+
+#[derive(TryScribeCowStr)]
 enum Airport {
     #[enumscribe(str = "LHR", case_insensitive)]
     Heathrow,
@@ -17,6 +18,8 @@ enum Airport {
 
 fn main() {
     let luton = Airport::Luton;
-    let luton_string = luton.try_scribe();
-    println!("Hello, {:?}!", luton_string);
+    println!("Hello, {:?}!", luton.try_scribe());
+
+    let other = Airport::Other("Dedicated EasyJet-only airport".to_owned());
+    println!("Hello, {:?}!", other.try_scribe());
 }