improve ergonomics for the derive macro generated api

bad-optics-derive/src/lib.rs

@@ -13,9 +13,10 @@ pub fn derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 
     let name = &input.ident;
     let mod_name = Ident::new(&get_mod_name(&input), Span::call_site());
+    let container_name = Ident::new(&get_container_name(&input), Span::call_site());
 
     let expanded = match input.data {
-        syn::Data::Struct(s) => expand_struct(s, name, &mod_name),
+        syn::Data::Struct(s) => expand_struct(s, name, &mod_name, &container_name),
         syn::Data::Enum(_) => todo!("not yet implemented for prisms"),
         syn::Data::Union(_) => panic!("this macro does not work on unions"),
     };
@@ -40,7 +41,28 @@ fn get_mod_name(input: &DeriveInput) -> String {
     input.ident.to_string().to_lowercase()
 }
 
-fn expand_struct(data: DataStruct, name: &Ident, mod_name: &Ident) -> TokenStream {
+fn get_container_name(input: &DeriveInput) -> String {
+    for i in &input.attrs {
+        if let Ok(Meta::NameValue(meta)) = i.parse_meta() {
+            if let Some(ident) = meta.path.get_ident() {
+                if ident == "container_name" {
+                    if let Lit::Str(a) = meta.lit {
+                        return a.value();
+                    }
+                }
+            }
+        }
+    }
+
+    format!("{}LensContainer", input.ident.to_string())
+}
+
+fn expand_struct(
+    data: DataStruct,
+    name: &Ident,
+    mod_name: &Ident,
+    container_name: &Ident,
+) -> TokenStream {
     let fields = match &data.fields {
         syn::Fields::Named(n) => n.named.iter(),
         syn::Fields::Unnamed(_) => todo!(),
@@ -87,8 +109,8 @@ fn expand_struct(data: DataStruct, name: &Ident, mod_name: &Ident) -> TokenStrea
                 .collect::<TokenStream>();
 
             quote! {
-                impl Lenses<#ty> {
+                impl bad_optics::has_lens::HasLensOf<#ty> for #name {
-                    pub fn get() ->
+                    fn get() ->
                           Vec<
                               bad_optics::lenses::Lens<
                                   bad_optics::lenses::lens_with_ref::LensWithRef<
@@ -113,12 +135,19 @@ fn expand_struct(data: DataStruct, name: &Ident, mod_name: &Ident) -> TokenStrea
         .collect::<TokenStream>();
 
     quote! {
-        pub mod #mod_name {
+        mod #mod_name {
             use super::*;
 
-            #lens_funcs
+            pub struct #container_name;
+
+            impl HasLens for #name {
+                type Lenses = #container_name;
+            }
+
+            impl #container_name {
+                #lens_funcs
+            }
 
-            pub struct Lenses<T>(std::marker::PhantomData<T>);
             #group_impls
         }
     }

examples/derive.rs

@@ -1,4 +1,7 @@
-use bad_optics::prelude::Optics;
+use bad_optics::prelude::*;
+
+#[macro_use]
+extern crate bad_optics;
 
 // the Optics derive macro will implement lenses for every public field in the struct
 // it makes a module named whatever the struct is called, but in lower case
@@ -26,20 +29,24 @@ fn main() {
     //
     // these lenses work for `MyStruct` with `view` and `over`,
     // and for `&MyStruct` with `view`
-    let field1 = mystruct::field1();
+    let field1 = <MyStruct as HasLens>::Lenses::field1();
-    let field2 = mystruct::field2();
+    // short macro for convenience, expands to the line above
+    let field2 = lens!(MyStruct::field2);
 
     // the lenses work normally as any other lens :)
     assert_eq!(field1(&o), "first field");
     assert_eq!(field2(&o), "second field");
 
     // we can get a vec with all the lenses that match a type
-    let string_lenses = mystruct::Lenses::<String>::get();
+    let string_lenses = <MyStruct as HasLensOf<String>>::get();
     assert_eq!(string_lenses.len(), 2);
 
     // since _field4 is private, there's no lens for it
-    let vec_string_lenses = mystruct::Lenses::<u8>::get();
+    let u8_lenses = <MyStruct as HasLensOf<u8>>::get();
-    assert_eq!(vec_string_lenses.len(), 1);
+    assert_eq!(u8_lenses.len(), 1);
+
+    // short macro for convenience, expands to the line above
+    let _u8_lenses = lenses!(MyStruct::u8);
 
     let mut o = o;
     for lens in string_lenses {

src/combinations.rs

@@ -144,8 +144,7 @@ where
     fn traverse(&self, thing: T) -> Vec<Self::Field> {
         let a = A::traverse(&self.0 .0, thing);
         a.into_iter()
-            .map(|v| B::traverse(&self.1 .0, v))
+            .flat_map(|v| B::traverse(&self.1 .0, v))
-            .flatten()
             .collect()
     }
 }

src/lib.rs

@@ -1,4 +1,5 @@
 #![feature(unboxed_closures, fn_traits, const_trait_impl)]
+#![allow(clippy::type_complexity)]
 
 pub mod combinations;
 mod fns;
@@ -14,4 +15,33 @@ pub mod prelude {
     pub use crate::lenses::*;
     pub use crate::prisms::*;
     pub use crate::traversals::*;
+
+    pub use crate::has_lens::*;
+}
+
+pub mod has_lens {
+    use crate::prelude::{lens::FuncLens, lens_with_ref::LensWithRef, to::ToRefInner};
+
+    use super::prelude::*;
+
+    pub trait HasLens {
+        type Lenses;
+    }
+
+    pub trait HasLensOf<T>: Sized {
+        fn get() -> Vec<Lens<LensWithRef<Lens<FuncLens<Self, T>>, Lens<ToRefInner<Self, T>>, Self>>>;
+    }
+
+    #[macro_export]
+    macro_rules! lens {
+        ($name:ident :: $func:ident) => {
+            <$name as HasLens>::Lenses::$func()
+        };
+    }
+    #[macro_export]
+    macro_rules! lenses {
+        ($name:ident :: $ty:ident) => {
+            <$name as HasLensOf<$ty>>::get()
+        };
+    }
 }

src/prisms/mod.rs

@@ -21,11 +21,7 @@ pub trait PrismPreview<T> {
         F: FnOnce(Self::Field) -> Self::Field,
         T: Clone,
     {
-        if let Some(a) = Self::preview(&self, thing.clone()) {
+        Self::preview(self, thing.clone()).map_or(thing, |a| Self::review(self, f(a)))
-            Self::review(&self, f(a))
-        } else {
-            thing
-        }
     }
 
     fn set(&self, thing: T, v: Self::Field) -> T
@@ -33,7 +29,7 @@ pub trait PrismPreview<T> {
         T: Clone,
         Self::Field: Clone,
     {
-        Self::over(self, thing, move |_| v.clone())
+        Self::over(self, thing, move |_| v)
     }
 }