glib: Implement enum paramspec builder variant that builds the default value automatically

Fixes #831

Author: sdroege

glib/src/param_spec.rs

@@ -1000,12 +1000,18 @@ impl ParamSpecEnum {
         }
     }
 
-    pub fn builder<T: StaticType + FromGlib<i32> + IntoGlib<GlibType = i32>>(
+    pub fn builder_with_default<T: StaticType + FromGlib<i32> + IntoGlib<GlibType = i32>>(
         name: &str,
         default_value: T,
     ) -> ParamSpecEnumBuilder<T> {
         ParamSpecEnumBuilder::new(name, default_value)
     }
+
+    pub fn builder<T: StaticType + FromGlib<i32> + IntoGlib<GlibType = i32> + Default>(
+        name: &str,
+    ) -> ParamSpecEnumBuilder<T> {
+        ParamSpecEnumBuilder::new(name, T::default())
+    }
 }
 
 #[must_use]

glib/src/subclass/mod.rs

@@ -100,10 +100,9 @@
 //!                 vec![
 //!                     glib::ParamSpecString::builder("name")
 //!                         .build(),
-//!                     glib::ParamSpecEnum::builder::<Animal>("animal", Animal::default())
+//!                     glib::ParamSpecEnum::builder::<Animal>("animal")
 //!                         .build(),
 //!                     glib::ParamSpecFlags::builder::<MyFlags>("flags")
-//!                         .default_value(MyFlags::default())
 //!                         .build(),
 //!                     glib::ParamSpecVariant::builder("variant", glib::VariantTy::ANY)
 //!                         .build(),