Enable as an inner type

Author: greyblake

CHANGELOG.md

@@ -1,6 +1,7 @@
 ### v0.x.x - 2025-xx-xx
-- **[FEATURE]** Ability to instantiate types in `const` context, when declared with `const_fn` flag.
 - **[BREAKING]** Fallible `::new()` constructor is removed (was deprecated in 0.4.3).
+- **[FEATURE]** Ability to instantiate types in `const` context, when declared with `const_fn` flag.
+- **[FIX]** Enable `&'a str` as an inner type.
 
 ### v0.5.1 - 2024-12-20
 

dummy/src/main.rs

@@ -1,23 +1,12 @@
 use nutype::nutype;
 
 #[nutype(
-    const_fn,
     derive(Debug),
-    validate(greater_or_equal = -273.15),
+    validate(predicate = |name| !name.trim().is_empty())
 )]
-pub struct Celsius(f64);
-
-macro_rules! nutype_const {
-    ($name:ident, $ty:ty, $value:expr) => {
-        const $name: $ty = match <$ty>::try_new($value) {
-            Ok(value) => value,
-            Err(_) => panic!("Invalid value"),
-        };
-    };
-}
-
-nutype_const!(WATER_BOILING_POINT, Celsius, 100.0);
+pub struct Name<'a>(&'a str);
 
 fn main() {
-    println!("{:?}", WATER_BOILING_POINT);
+    let name_error = Name::try_new("  ").unwrap_err();
+    assert_eq!(name_error, NameError::PredicateViolated);
 }

nutype_macros/src/common/parse/meta.rs

@@ -65,18 +65,7 @@ pub fn parse_meta(token_stream: TokenStream) -> Result<Meta, syn::Error> {
     })?;
     validate_inner_field_visibility(&seg.vis)?;
 
-    let type_path = match seg.ty.clone() {
-        syn::Type::Path(tp) => tp,
-        _ => {
-            let error = syn::Error::new(
-                seg.span(),
-                "#[nutype] requires a simple inner type (e.g. String, i32, etc.)",
-            );
-            return Err(error);
-        }
-    };
-
-    let type_path_str = type_path.into_token_stream().to_string();
+    let type_path_str = seg.ty.clone().into_token_stream().to_string();
 
     let inner_type = match type_path_str.as_ref() {
         "String" => InnerType::String(StringInnerType),

test_suite/tests/any.rs

@@ -1045,3 +1045,26 @@ mod constants {
         assert_eq!(VALID.as_ref().y, 10);
     }
 }
+
+mod str_reference {
+    use nutype::nutype;
+
+    #[nutype(
+        derive(Debug),
+        validate(predicate = |name| !name.trim().is_empty())
+    )]
+    pub struct Name<'a>(&'a str);
+
+    #[test]
+    fn test_validation_of_str_reference() {
+        {
+            let name_error = Name::try_new("  ").unwrap_err();
+            assert_eq!(name_error, NameError::PredicateViolated);
+        }
+
+        {
+            let name = Name::try_new("John").unwrap();
+            assert_eq!(name.into_inner(), "John");
+        }
+    }
+}