add Null and TryNull traits

Signed-off-by: Dave Huseby <dwh@linuxprogrammer.org>

Cargo.toml

@@ -1,8 +1,8 @@
 [package]
 name = "multitrait"
-version = "0.1.9"
+version = "0.1.10"
 edition = "2021"
-authors = ["Dave Huseby <dwh@linuxprogrammer.org>"]
+authors = ["Dave Grantham <dwg@linuxprogrammer.org>"]
 description = "Common traits for multiformats types"
 repository = "https://github.com/cryptidtech/multitrait.git"
 readme = "README.md"

src/lib.rs

@@ -25,13 +25,17 @@ pub use error::Error;
 pub mod enc_into;
 pub use enc_into::EncodeInto;
 
+/// Null and TryNull traits
+pub mod null;
+pub use null::{Null, TryNull};
+
 /// TryDecodeFrom trait
 pub mod try_decode_from;
 pub use try_decode_from::TryDecodeFrom;
 
 /// one-stop shop for all exported symbols
 pub mod prelude {
-    pub use super::{enc_into::*, try_decode_from::*};
+    pub use super::{enc_into::*, null::*, try_decode_from::*};
 }
 
 #[cfg(test)]
@@ -98,4 +102,38 @@ mod test {
         let (num, _) = usize::try_decode_from(&buf).unwrap();
         assert_eq!(0xffeeddcc_usize, num);
     }
+
+    struct Foo(usize);
+
+    impl Null for Foo {
+        fn null() -> Self {
+            Foo(0)
+        }
+        fn is_null(&self) -> bool {
+            self.0 == 0
+        }
+    }
+
+    impl TryNull for Foo {
+        type Error = &'static str;
+
+        fn try_null() -> Result<Self, Self::Error> {
+            Ok(Foo(0))
+        }
+        fn is_null(&self) -> bool {
+            self.0 == 0
+        }
+    }
+
+    #[test]
+    fn test_null_value() {
+        let f = Foo::null();
+        assert!(Null::is_null(&f));
+    }
+
+    #[test]
+    fn test_try_null_value() {
+        let f = Foo::try_null().unwrap();
+        assert!(TryNull::is_null(&f));
+    }
 }

src/null.rs

@@ -0,0 +1,18 @@
+/// This trait is for multiformat objects that have a NULL value
+pub trait Null {
+    /// return an instance of Self where is_null(&self) -> true
+    fn null() -> Self;
+    /// verify if self is the null value
+    fn is_null(&self) -> bool;
+}
+
+/// This trait is a fallible version of Null
+pub trait TryNull: Sized {
+    /// the error type to return when constructing a null value fails
+    type Error;
+
+    /// try to construct a Null value of Self 
+    fn try_null() -> Result<Self, Self::Error>;
+    /// verify if self is the null value
+    fn is_null(&self) -> bool;
+}