Expose derived lenses as associated constants

Author: Ralith

README.md

@@ -188,7 +188,8 @@ struct AppState {
 ### lens
 
 The [Lens datatype] gives access to a part of a larger data structure. Like
-`Data`, This can be derived.
+`Data`, this can be derived. Derived lenses are accessed as associated constants
+with the same name as the field.
 
 ```rust
 #[derive(Clone, Data, Lens)]
@@ -202,7 +203,7 @@ To use the lens, wrap your widget with `LensWrap` (note the conversion of
 CamelCase to snake_case):
 
 ```rust
-LensWrap::new(WidgetThatExpectsf64::new(), app_state::value);
+LensWrap::new(WidgetThatExpectsf64::new(), AppState::value);
 ```
 
 ## Using druid

druid-derive/src/lens.rs

@@ -48,7 +48,7 @@ fn derive_struct(input: &syn::DeriveInput) -> Result<proc_macro2::TokenStream, s
     };
 
     let twizzled_name = if is_camel_case(&ty.to_string()) {
-        let temp_name = to_snake_case(&ty.to_string());
+        let temp_name = format!("{}_derived_lenses", to_snake_case(&ty.to_string()));
         proc_macro2::Ident::new(&temp_name, proc_macro2::Span::call_site())
     } else {
         return Err(syn::Error::new(
@@ -57,22 +57,15 @@ fn derive_struct(input: &syn::DeriveInput) -> Result<proc_macro2::TokenStream, s
         ));
     };
 
-    // Declare a struct for each field
-    let structs = fields.iter().map(|f| {
-        let field_name = &f.ident;
-
-        quote! {
-            #[allow(non_camel_case_types)]
-            pub struct #field_name;
-        }
-    });
-
     // Impl Lens for each field
     let impls = fields.iter().map(|f| {
         let field_name = &f.ident;
         let field_ty = &f.ty;
 
         quote! {
+            /// Lens for the field on #ty
+            #[allow(non_camel_case_types)]
+            pub struct #field_name;
 
             impl Lens<#ty, #field_ty> for #field_name {
                 fn with<V, F: FnOnce(&#field_ty) -> V>(&self, data: &#ty, f: F) -> V {
@@ -86,13 +79,26 @@ fn derive_struct(input: &syn::DeriveInput) -> Result<proc_macro2::TokenStream, s
         }
     });
 
+    let associated_items = fields.iter().map(|f| {
+        let field_name = &f.ident;
+        quote! {
+            /// Lens for the corresponding field
+            pub const #field_name: #field_name = #field_name;
+        }
+    });
+
     let expanded = quote! {
         pub mod #twizzled_name {
+            //! Lens definitions for #ty
             use super::*;
-
             use druid::Lens;
-            #(#structs)*
+
             #(#impls)*
+
+            #[allow(non_upper_case_globals)]
+            impl #ty {
+                #(#associated_items)*
+            }
         }
     };
 

druid-derive/src/lib.rs

@@ -31,6 +31,10 @@ pub fn derive_data(input: TokenStream) -> TokenStream {
         .into()
 }
 
+/// Generates lenses to access the fields of a struct
+///
+/// An associated constant is defined on the struct for each field,
+/// having the same name as the field.
 #[proc_macro_derive(Lens)]
 pub fn derive_lens(input: TokenStream) -> TokenStream {
     let input = parse_macro_input!(input as syn::DeriveInput);

druid/examples/calc.rs

@@ -152,7 +152,7 @@ fn build_calc() -> impl Widget<CalcState> {
     let mut column = Flex::column();
     let display = LensWrap::new(
         DynLabel::new(|data: &String, _env| data.clone()),
-        calc_state::value,
+        CalcState::value,
     );
     column.add_child(pad(display), 0.0);
     column.add_child(

druid/examples/either.rs

@@ -35,12 +35,12 @@ fn ui_builder() -> impl Widget<AppState> {
 
     let mut col = Flex::column();
     col.add_child(
-        Padding::new(5.0, LensWrap::new(Checkbox::new(), app_state::which)),
+        Padding::new(5.0, LensWrap::new(Checkbox::new(), AppState::which)),
         0.0,
     );
     let either = Either::new(
         |data, _env| data.which,
-        Padding::new(5.0, LensWrap::new(Slider::new(), app_state::value)),
+        Padding::new(5.0, LensWrap::new(Slider::new(), AppState::value)),
         Padding::new(5.0, label),
     );
     col.add_child(either, 0.0);

druid/examples/slider.rs

@@ -31,13 +31,13 @@ fn build_widget() -> impl Widget<DemoState> {
         }
     });
     let mut row = Flex::row();
-    let checkbox = LensWrap::new(Checkbox::new(), demo_state::double);
+    let checkbox = LensWrap::new(Checkbox::new(), DemoState::double);
     let checkbox_label = Label::new("double the value");
     row.add_child(checkbox, 0.0);
     row.add_child(Padding::new(5.0, checkbox_label), 1.0);
 
-    let bar = LensWrap::new(ProgressBar::new(), demo_state::value);
-    let slider = LensWrap::new(Slider::new(), demo_state::value);
+    let bar = LensWrap::new(ProgressBar::new(), DemoState::value);
+    let slider = LensWrap::new(Slider::new(), DemoState::value);
 
     let button_1 = Button::sized(
         "increment ",

druid/examples/switch.rs

@@ -23,7 +23,7 @@ struct DemoState {
 fn build_widget() -> impl Widget<DemoState> {
     let mut col = Flex::column();
     let mut row = Flex::row();
-    let switch = LensWrap::new(Switch::new(), demo_state::value);
+    let switch = LensWrap::new(Switch::new(), DemoState::value);
     let switch_label = Label::new("Setting label");
 
     row.add_child(Padding::new(5.0, switch_label), 0.0);