Deduplicate recurring logic

Author: Oliver Scherer

src/lib.rs

@@ -165,16 +165,11 @@ fn newtype_inner(data: &syn::Data) -> Option<syn::Type> {
 pub fn from_primitive(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
 
     let impl_ = if let Some(inner_ty) = newtype_inner(&ast.data) {
-        let bound = quote! { #inner_ty: _num_traits::FromPrimitive };
-        let where_ = match where_ {
-            Some(where_) => quote!{ #where_, #bound },
-            None => quote!{ where #bound },
-        };
         quote! {
-            impl #impl_ _num_traits::FromPrimitive for #name #type_ #where_ {
+            impl #impl_ _num_traits::FromPrimitive for #name #type_ #where_ #inner_ty: _num_traits::FromPrimitive {
                 fn from_i64(n: i64) -> Option<Self> {
                     <#inner_ty as _num_traits::FromPrimitive>::from_i64(n).map(#name)
                 }
@@ -327,16 +322,11 @@ pub fn from_primitive(input: TokenStream) -> TokenStream {
 pub fn to_primitive(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
 
     let impl_ = if let Some(inner_ty) = newtype_inner(&ast.data) {
-        let bound = quote! { #inner_ty: _num_traits::ToPrimitive };
-        let where_ = match where_ {
-            Some(where_) => quote!{ #where_, #bound },
-            None => quote!{ where #bound },
-        };
         quote! {
-            impl #impl_ _num_traits::ToPrimitive for #name #type_ #where_ {
+            impl #impl_ _num_traits::ToPrimitive for #name #type_ #where_ #inner_ty: _num_traits::ToPrimitive {
                 fn to_i64(&self) -> Option<i64> {
                     <#inner_ty as _num_traits::ToPrimitive>::to_i64(&self.0)
                 }
@@ -452,12 +442,8 @@ const NEWTYPE_ONLY: &str = "This trait can only be derived for newtypes";
 pub fn num_ops(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
     let inner_ty = newtype_inner(&ast.data).expect(NEWTYPE_ONLY);
-    let where_ = match where_ {
-        Some(where_) => quote!{ #where_, },
-        None => quote!{ where },
-    };
     dummy_const_trick(
         "NumOps",
         &name,
@@ -505,12 +491,8 @@ pub fn num_ops(input: TokenStream) -> TokenStream {
 pub fn num_cast(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
     let inner_ty = newtype_inner(&ast.data).expect(NEWTYPE_ONLY);
-    let where_ = match where_ {
-        Some(where_) => quote!{ #where_,  },
-        None => quote!{ where },
-    };
     let fn_param = proc_macro2::Ident::new("FROM_T", name.span());
     dummy_const_trick(
         "NumCast",
@@ -534,12 +516,8 @@ pub fn num_cast(input: TokenStream) -> TokenStream {
 pub fn zero(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
     let inner_ty = newtype_inner(&ast.data).expect(NEWTYPE_ONLY);
-    let where_ = match where_ {
-        Some(where_) => quote!{ #where_, },
-        None => quote!{ where },
-    };
     dummy_const_trick(
         "Zero",
         &name,
@@ -564,12 +542,8 @@ pub fn zero(input: TokenStream) -> TokenStream {
 pub fn one(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
     let inner_ty = newtype_inner(&ast.data).expect(NEWTYPE_ONLY);
-    let where_ = match where_ {
-        Some(where_) => quote!{ #where_, },
-        None => quote!{ where },
-    };
     dummy_const_trick(
         "One",
         &name,
@@ -587,19 +561,24 @@ pub fn one(input: TokenStream) -> TokenStream {
     .into()
 }
 
+fn split_for_impl(generics: &syn::Generics) -> (syn::ImplGenerics, syn::TypeGenerics, impl quote::ToTokens) {
+    let (impl_, type_, where_) = generics.split_for_impl();
+    let where_ = match where_ {
+        Some(where_) => quote!{ #where_, },
+        None => quote!{ where },
+    };
+    (impl_, type_, where_)
+}
+
 /// Derives [`num_traits::Num`][num] for newtypes.  The inner type must already implement `Num`.
 ///
 /// [num]: https://docs.rs/num-traits/0.2/num_traits/trait.Num.html
 #[proc_macro_derive(Num)]
 pub fn num(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
     let inner_ty = newtype_inner(&ast.data).expect(NEWTYPE_ONLY);
-    let where_ = match where_ {
-        Some(where_) => quote!{ #where_, },
-        None => quote!{ where },
-    };
     dummy_const_trick(
         "Num",
         &name,
@@ -623,12 +602,8 @@ pub fn num(input: TokenStream) -> TokenStream {
 pub fn float(input: TokenStream) -> TokenStream {
     let ast: syn::DeriveInput = syn::parse(input).unwrap();
     let name = &ast.ident;
-    let (impl_, type_, where_) = &ast.generics.split_for_impl();
+    let (impl_, type_, where_) = split_for_impl(&ast.generics);
     let inner_ty = newtype_inner(&ast.data).expect(NEWTYPE_ONLY);
-    let where_ = match where_ {
-        Some(where_) => quote!{ #where_, },
-        None => quote!{ where },
-    };
     dummy_const_trick(
         "Float",
         &name,