feat(pickable): extract SinglePickable into its own module

2 files changed, 72 insertions, 44 deletions

diff --git a/mingling_picker/src/pickable.rs b/mingling_picker/src/pickable.rs
index 7424e6f..463edc0 100644
--- a/mingling_picker/src/pickable.rs
+++ b/mingling_picker/src/pickable.rs
@@ -1,5 +1,8 @@
 use crate::{PickerArg, PickerArgAttr, PickerArgInfo, PickerArgResult, PickerArgs};
 
+mod single_pickable;
+pub use single_pickable::*;
+
 /// `Pickable` trait defines how to parse a type instance from command-line arguments.
 ///
 /// This trait is the core abstraction of the `Picker` argument parsing system, dividing the
@@ -83,47 +86,3 @@ pub struct TagPhaseContext<'a> {
     /// has already been tagged by another `Pickable`.
     pub mask: &'a [u8],
 }
-
-/// `SinglePickable` trait defines how to parse a type from a single command-line argument.
-///
-/// This trait provides a simplified interface for types that consume exactly one argument value.
-/// It is automatically implemented by the blanket `impl` of [`Pickable`], so types implementing
-/// `SinglePickable` will work with the full `Pickable` argument parsing system.
-///
-/// # Type Parameters
-///
-/// * `Self` - The type to be parsed from a single argument string.
-pub trait SinglePickable
-where
-    Self: Sized,
-{
-    /// Parse a single optional string value into an instance of `Self`.
-    ///
-    /// # Parameters
-    ///
-    /// * `str` - An `Option<&str>` representing the raw argument value. If `None`,
-    ///   it indicates that no argument value was provided (e.g., for flag-like arguments).
-    ///
-    /// # Returns
-    ///
-    /// Returns [`PickerArgResult<Self>`], i.e., the parsed `Self` instance on success,
-    /// or an appropriate error message on failure.
-    fn pick_single(str: Option<&str>) -> PickerArgResult<Self>;
-}
-
-impl<'a, S> Pickable<'a> for S
-where
-    S: SinglePickable,
-{
-    fn get_attr(flag: &'a PickerArg<'a, Self>) -> PickerArgAttr {
-        PickerArgAttr::positional_or_single(flag)
-    }
-
-    fn tag(ctx: TagPhaseContext) -> Vec<usize> {
-        crate::parselib::SingleMatcher::tag(ctx)
-    }
-
-    fn pick(raw_strs: &[&str]) -> PickerArgResult<Self> {
-        Self::pick_single(crate::parselib::seek_single(raw_strs))
-    }
-}
diff --git a/mingling_picker/src/pickable/single_pickable.rs b/mingling_picker/src/pickable/single_pickable.rs
new file mode 100644
index 0000000..8a5b3e6
--- /dev/null
+++ b/mingling_picker/src/pickable/single_pickable.rs
@@ -0,0 +1,69 @@
+use crate::{Pickable, PickerArg, PickerArgAttr, PickerArgResult, TagPhaseContext};
+
+/// `SinglePickable` trait defines how to parse a type from a single command-line argument.
+///
+/// This trait provides a simplified interface for types that consume exactly one argument value.
+/// It is automatically implemented by the blanket `impl` of [`Pickable`], so types implementing
+/// `SinglePickable` will work with the full `Pickable` argument parsing system.
+///
+/// Additionally, `Option<S>` where `S: SinglePickable` also implements [`Pickable`], allowing
+/// optional arguments to be parsed naturally.
+///
+/// # Type Parameters
+///
+/// * `Self` - The type to be parsed from a single argument string.
+pub trait SinglePickable
+where
+    Self: Sized,
+{
+    /// Parse a single optional string value into an instance of `Self`.
+    ///
+    /// # Parameters
+    ///
+    /// * `str` - An `Option<&str>` representing the raw argument value. If `None`,
+    ///   it indicates that no argument value was provided (e.g., for flag-like arguments).
+    ///
+    /// # Returns
+    ///
+    /// Returns [`PickerArgResult<Self>`], i.e., the parsed `Self` instance on success,
+    /// or an appropriate error message on failure.
+    fn pick_single(str: Option<&str>) -> PickerArgResult<Self>;
+}
+
+impl<'a, S> Pickable<'a> for S
+where
+    S: SinglePickable,
+{
+    fn get_attr(flag: &'a PickerArg<'a, Self>) -> PickerArgAttr {
+        PickerArgAttr::positional_or_single(flag)
+    }
+
+    fn tag(ctx: TagPhaseContext) -> Vec<usize> {
+        crate::parselib::SingleMatcher::tag(ctx)
+    }
+
+    fn pick(raw_strs: &[&str]) -> PickerArgResult<Self> {
+        Self::pick_single(crate::parselib::seek_single(raw_strs))
+    }
+}
+
+impl<'a, S> Pickable<'a> for Option<S>
+where
+    S: SinglePickable,
+{
+    fn get_attr(flag: &'a PickerArg<'a, Self>) -> PickerArgAttr {
+        PickerArgAttr::positional_or_single(flag)
+    }
+
+    fn tag(ctx: TagPhaseContext) -> Vec<usize> {
+        crate::parselib::SingleMatcher::tag(ctx)
+    }
+
+    fn pick(raw_strs: &[&str]) -> PickerArgResult<Self> {
+        match S::pick(raw_strs) {
+            PickerArgResult::Unparsed => PickerArgResult::Unparsed,
+            PickerArgResult::Parsed(r) => PickerArgResult::Parsed(Some(r)),
+            PickerArgResult::NotFound => PickerArgResult::Parsed(None),
+        }
+    }
+}