refactor: Conversion from row id to usize is now fallible. (#319)

BREAKING CHANGE: TryFrom replaces From.

Author: molpopgen

examples/forward_simulation.rs

@@ -368,9 +368,9 @@ fn simplify(
         Ok(x) => match x {
             Some(idmap) => {
                 for a in alive.iter_mut() {
-                    a.node0 = idmap[usize::from(a.node0)];
+                    a.node0 = idmap[usize::try_from(a.node0).unwrap()];
                     assert!(a.node0 != tskit::NodeId::NULL);
-                    a.node1 = idmap[usize::from(a.node1)];
+                    a.node1 = idmap[usize::try_from(a.node1).unwrap()];
                     assert!(a.node1 != tskit::NodeId::NULL);
                 }
             }

src/_macros.rs

@@ -248,9 +248,16 @@ macro_rules! impl_id_traits {
             }
         }
 
-        impl From<$idtype> for usize {
-            fn from(value: $idtype) -> Self {
-                value.0 as usize
+        impl TryFrom<$idtype> for usize {
+            type Error = crate::TskitError;
+            fn try_from(value: $idtype) -> Result<Self, Self::Error> {
+                match value.0.try_into() {
+                    Ok(value) => Ok(value),
+                    Err(_) => Err(crate::TskitError::RangeError(format!(
+                        "could not convert {:?} to usize",
+                        value
+                    ))),
+                }
             }
         }
 

src/test_simplification.rs

@@ -37,7 +37,7 @@ mod tests {
         assert!(idmap_option.is_some());
         let idmap = idmap_option.unwrap();
         for &i in samples {
-            assert_ne!(idmap[usize::from(i)], NodeId::NULL);
+            assert_ne!(idmap[usize::try_from(i).unwrap()], NodeId::NULL);
         }
     }
 }