Add Flagged struct

Requires enumflags2 as a dependency. Can't reexport it since the
bitflags macro is not hygienic (see meithecatte/enumflags2#48).

Cargo.toml

@@ -5,3 +5,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+enumflags2 = "0.7.9"

src/lib.rs

@@ -1,14 +1,54 @@
-pub fn add(left: usize, right: usize) -> usize {
-    left + right
+use enumflags2::{BitFlag, BitFlags};
+
+#[derive(Debug, Clone, Copy)]
+pub struct Flagged<T, F: BitFlag> {
+    pub value: T,
+    pub flags: BitFlags<F>,
+}
+
+impl<T, F: BitFlag> Flagged<T, F> {
+    pub fn and_then<U>(self, f: impl FnOnce(T) -> Flagged<U, F>) -> Flagged<U, F> {
+        let inner = f(self.value);
+        Flagged {
+            value: inner.value,
+            flags: self.flags | inner.flags, //merge flags
+        }
+    }
+
+    pub fn into_result(self) -> Result<T, BitFlags<F>> {
+        if self.flags != BitFlags::EMPTY {
+            Err(self.flags)
+        } else {
+            Ok(self.value)
+        }
+    }
+
+    pub fn into_result_against(self, flags: BitFlags<F>) -> Result<T, BitFlags<F>> {
+        if self.flags.intersects(flags) {
+            Err(self.flags & flags) //only include error flags
+        } else {
+            Ok(self.value)
+        }
+    }
 }
 
-#[cfg(test)]
-mod tests {
-    use super::*;
+impl<T, F: BitFlag> From<T> for Flagged<T, F> {
+    fn from(value: T) -> Self {
+        Self {
+            value,
+            flags: BitFlags::EMPTY,
+        }
+    }
+}
 
-    #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
+impl<T, F: BitFlag> FromIterator<Flagged<T, F>> for Flagged<Vec<T>, F> {
+    fn from_iter<I: IntoIterator<Item = Flagged<T, F>>>(iter: I) -> Self {
+        let mut value = vec![];
+        let mut flags = BitFlags::EMPTY;
+        for flagged in iter {
+            value.push(flagged.value);
+            flags |= flagged.flags;
+        }
+        Self { value, flags }
     }
 }