Add conversion attribute to optionally implement From/Into underlying…

… type (#62)

README.md

@@ -22,6 +22,7 @@ println!("{}", timestamp); // Timestamp(1701620628123456789)
   - Adding the following attributes to `#[strong_type(...)]` allows for additional features:
     - `auto_operators`: Automatically implements relevant arithmetic (for numeric types) or logical (for boolean types) operators.
     - `custom_display`: Allows users to manually implement the `Display` trait, providing an alternative to the default display format.
+    - `conversion`: Automatically implements `From` and `Into` traits for the underlying type.
     - `underlying`: Specifies the underlying primitive type for nested strong types.
 
 ## Installation

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

@@ -0,0 +1,28 @@
+use proc_macro2::TokenStream;
+use quote::quote;
+
+pub(crate) fn implement_conversion(name: &syn::Ident, value_type: &syn::Ident) -> TokenStream {
+    quote! {
+        impl From<#value_type> for #name {
+            fn from(value: #value_type) -> Self {
+                Self::new(value)
+            }
+        }
+
+        impl From<#name> for #value_type {
+            fn from(value: #name) -> #value_type {
+                value.0
+            }
+        }
+    }
+}
+
+pub(crate) fn implement_str_conversion(name: &syn::Ident) -> TokenStream {
+    quote! {
+        impl From<&str> for #name {
+            fn from(value: &str) -> Self {
+                Self::new(value)
+            }
+        }
+    }
+}

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

@@ -5,6 +5,7 @@ mod basic_string;
 mod bit_ops;
 mod bool_ops;
 mod constants;
+mod conversion;
 mod display;
 mod hash;
 mod nan;
@@ -26,6 +27,7 @@ pub(crate) use bool_ops::implement_bool_ops;
 pub(crate) use constants::{
     implement_constants, implement_constants_derived, implement_infinity, implement_limit,
 };
+pub(crate) use conversion::{implement_conversion, implement_str_conversion};
 pub(crate) use display::implement_display;
 pub(crate) use hash::implement_hash;
 pub(crate) use nan::implement_nan;

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

@@ -5,13 +5,15 @@ use syn::{Data, DeriveInput, Fields, Visibility};
 pub(crate) struct StrongTypeAttributes {
     pub has_auto_operators: bool,
     pub has_custom_display: bool,
+    pub has_conversion: bool,
     pub type_info: TypeInfo,
 }
 
 pub(crate) fn get_attributes(input: &DeriveInput) -> StrongTypeAttributes {
     let mut attributes = StrongTypeAttributes {
         has_auto_operators: false,
         has_custom_display: false,
+        has_conversion: false,
         type_info: get_type(input),
     };
 
@@ -24,6 +26,9 @@ pub(crate) fn get_attributes(input: &DeriveInput) -> StrongTypeAttributes {
                 } else if meta.path.is_ident("custom_display") {
                     attributes.has_custom_display = true;
                     Ok(())
+                } else if meta.path.is_ident("conversion") {
+                    attributes.has_conversion = true;
+                    Ok(())
                 } else if meta.path.is_ident("underlying") {
                     if let Ok(strm) = meta.value() {
                         if let Ok(primitive_type) = strm.parse::<syn::Ident>() {
@@ -35,7 +40,7 @@ pub(crate) fn get_attributes(input: &DeriveInput) -> StrongTypeAttributes {
                     }
                     Ok(())
                 } else {
-                    Err(meta.error(format!("Invalid strong_type attribute {}, should be one of {{auto_operators, custom_display, underlying=type}}",
+                    Err(meta.error(format!("Invalid strong_type attribute {}, should be one of {{auto_operators, custom_display, conversion, underlying=type}}",
                                            meta.path.get_ident().expect("Failed to parse strong_type attributes."))))
                 }
             }) {

strong-type-derive/src/strong_type.rs

@@ -1,11 +1,12 @@
 use crate::detail::{
     get_attributes, implement_arithmetic, implement_basic, implement_basic_primitive,
     implement_basic_string, implement_bit_shift, implement_bool_ops, implement_constants,
-    implement_constants_derived, implement_display, implement_hash, implement_infinity,
-    implement_limit, implement_nan, implement_negate, implement_primitive_accessor,
-    implement_primitive_accessor_derived, implement_primitive_str_accessor,
-    implement_primitive_str_accessor_derived, is_struct_valid, StrongTypeAttributes, TypeInfo,
-    UnderlyingType, ValueTypeGroup,
+    implement_constants_derived, implement_conversion, implement_display, implement_hash,
+    implement_infinity, implement_limit, implement_nan, implement_negate,
+    implement_primitive_accessor, implement_primitive_accessor_derived,
+    implement_primitive_str_accessor, implement_primitive_str_accessor_derived,
+    implement_str_conversion, is_struct_valid, StrongTypeAttributes, TypeInfo, UnderlyingType,
+    ValueTypeGroup,
 };
 use proc_macro2::TokenStream;
 use quote::quote;
@@ -20,6 +21,7 @@ pub(super) fn expand_strong_type(input: DeriveInput) -> TokenStream {
     let StrongTypeAttributes {
         has_auto_operators,
         has_custom_display,
+        has_conversion,
         type_info:
             TypeInfo {
                 primitive_type,
@@ -37,6 +39,13 @@ pub(super) fn expand_strong_type(input: DeriveInput) -> TokenStream {
         ast.extend(implement_display(name));
     };
 
+    if has_conversion {
+        ast.extend(implement_conversion(name, &value_type));
+        if let ValueTypeGroup::String(UnderlyingType::Primitive) = &type_group {
+            ast.extend(implement_str_conversion(name));
+        }
+    }
+
     match &type_group {
         ValueTypeGroup::Int(underlying_type)
         | ValueTypeGroup::UInt(underlying_type)

strong-type-tests/tests/conversion.rs

@@ -0,0 +1,33 @@
+#[cfg(test)]
+mod tests {
+    use std::fmt::Debug;
+    use strong_type::StrongType;
+
+    fn test<T: Debug + Eq>(value: T, underlying: T) {
+        assert_eq!(value, underlying);
+    }
+
+    #[test]
+    fn test_conversion() {
+        #[derive(StrongType)]
+        #[strong_type(conversion)]
+        struct NamedI32(i64);
+
+        let i64_value = 64;
+        let value = NamedI32::new(i64_value);
+
+        test(value, i64_value.into());
+        test(value.into(), i64_value);
+
+        #[derive(StrongType)]
+        #[strong_type(conversion)]
+        struct NamedString(String);
+        let str_value = "test";
+        let string_value = String::from(str_value);
+        let value = NamedString::new(string_value.clone());
+
+        test(value.clone(), str_value.into());
+        test(value.clone(), string_value.clone().into());
+        test(value.into(), string_value);
+    }
+}

strong-type-tests/tests/tests.rs

@@ -1,4 +1,5 @@
 mod auto_operators;
+mod conversion;
 mod custom_underlying;
 mod display;
 mod strong_type;