add ::venndb::Any trait + example

README.md

@@ -94,7 +94,7 @@ pub struct Employee {
     is_admin: bool,
     #[venndb(skip)]
     foo: bool,
-    #[venndb(filter)]
+    #[venndb(filter, any)]
     department: Department,
     #[venndb(filter)]
     country: Option<String>,

src/lib.rs

@@ -2,6 +2,33 @@
 
 pub use venndb_macros::VennDB;
 
+/// A trait that types can implement in order to support `#[venndb(any)]` attribute filters.
+pub trait Any {
+    /// Returns true if the value is considered to be "any" within the context of the type.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use venndb::Any;
+    ///
+    /// #[derive(Debug)]
+    /// struct MyString(String);
+    ///
+    /// impl Any for MyString {
+    ///    fn is_any(&self) -> bool {
+    ///       self.0 == "*"
+    ///   }
+    /// }
+    ///
+    /// let my_string = MyString("*".to_string());
+    /// assert!(my_string.is_any());
+    ///
+    /// let my_string = MyString("hello".to_string());
+    /// assert!(!my_string.is_any());
+    /// ```
+    fn is_any(&self) -> bool;
+}
+
 #[doc(hidden)]
 pub mod __internal {
     //! Hidden thirdparty dependencies for venndb,

www/index.html

@@ -123,7 +123,7 @@ <h2>Example</h2>
     is_admin: bool,
     #[venndb(skip)]
     foo: bool,
-    #[venndb(filter)]
+    #[venndb(filter, any)]
     department: Department,
     #[venndb(filter)]
     country: Option&lt;String&gt;,