Add const_new to create compile-time constants (#60)

README.md

@@ -49,6 +49,7 @@ use strong_type::StrongType;
 struct Tag(String);
 
 let tag = Tag::new("dev");
+const TAG: Tag = Tag::const_new("prod");
 ```
 
 #### Demonstrating type distinctiveness:

strong-type-derive/src/detail/basic.rs

@@ -11,12 +11,15 @@ pub(crate) fn implement_basic(
             pub fn new(value: impl Into<#value_type>) -> Self {
                 Self(value.into())
             }
+
+            pub const fn const_new(value: #value_type) -> Self {
+                Self(value)
+            }
         }
 
         impl StrongType for #name {
             type UnderlyingType = #value_type;
             type PrimitiveType = #primitive_type;
-
         }
 
         impl std::fmt::Debug for #name {

strong-type-tests/tests/strong_type.rs

@@ -263,4 +263,14 @@ mod tests {
             }
         }
     }
+
+    #[test]
+    fn test_const() {
+        #[derive(StrongType)]
+        struct NamedI32(i32);
+
+        const NAMED_I32: NamedI32 = NamedI32::const_new(1);
+
+        assert_eq!(NAMED_I32, NamedI32::new(1));
+    }
 }