impl Display and Error for all error types

src/error.rs

@@ -0,0 +1,159 @@
+use std::fmt;
+use std::error::Error;
+
+/// The possible error conditions that `Solver::add_constraint` can fail with.
+#[derive(Debug, Copy, Clone)]
+pub enum AddConstraintError {
+    /// The constraint specified has already been added to the solver.
+    DuplicateConstraint,
+    /// The constraint is required, but it is unsatisfiable in conjunction with the existing constraints.
+    UnsatisfiableConstraint,
+    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
+    /// additional details as a string.
+    InternalSolverError(&'static str)
+}
+
+impl fmt::Display for AddConstraintError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let AddConstraintError::InternalSolverError(msg) = self {
+            write!(f, "internal solver error '{}'", msg)
+        } else {
+            write!(f, "{}", self.description())
+        }
+    }
+}
+
+impl Error for AddConstraintError {
+    fn description(&self) -> &str {
+        match self {
+            AddConstraintError::DuplicateConstraint => 
+                "constraint already added to the solver",
+            AddConstraintError::UnsatisfiableConstraint => 
+                "could not satisfy all required constraints",
+            AddConstraintError::InternalSolverError(_) => 
+                "internal solver error",
+        }
+    }
+}
+
+/// The possible error conditions that `Solver::remove_constraint` can fail with.
+#[derive(Debug, Copy, Clone)]
+pub enum RemoveConstraintError {
+    /// The constraint specified was not already in the solver, so cannot be removed.
+    UnknownConstraint,
+    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
+    /// additional details as a string.
+    InternalSolverError(&'static str)
+}
+
+impl fmt::Display for RemoveConstraintError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let RemoveConstraintError::InternalSolverError(msg) = self {
+            write!(f, "internal solver error '{}'", msg)
+        } else {
+            write!(f, "{}", self.description())
+        }
+    }
+}
+
+impl Error for RemoveConstraintError {
+    fn description(&self) -> &str {
+        match self {
+            RemoveConstraintError::UnknownConstraint => 
+                "constraint is not in the solver",
+            RemoveConstraintError::InternalSolverError(_) => 
+                "internal solver error",
+        }
+    }
+}
+
+/// The possible error conditions that `Solver::add_edit_variable` can fail with.
+#[derive(Debug, Copy, Clone)]
+pub enum AddEditVariableError {
+    /// The specified variable is already marked as an edit variable in the solver.
+    DuplicateEditVariable,
+    /// The specified strength was `REQUIRED`. This is illegal for edit variable strengths.
+    BadRequiredStrength
+}
+
+impl fmt::Display for AddEditVariableError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.description())
+    }
+}
+
+impl Error for AddEditVariableError {
+    fn description(&self) -> &str {
+        match self {
+            AddEditVariableError::DuplicateEditVariable =>
+                "variable already marked as an edit variable",
+            AddEditVariableError::BadRequiredStrength => 
+                "invalid strength for edit variable",
+        }
+    }
+}
+
+/// The possible error conditions that `Solver::remove_edit_variable` can fail with.
+#[derive(Debug, Copy, Clone)]
+pub enum RemoveEditVariableError {
+    /// The specified variable was not an edit variable in the solver, so cannot be removed.
+    UnknownEditVariable,
+    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
+    /// additional details as a string.
+    InternalSolverError(&'static str)
+}
+
+impl fmt::Display for RemoveEditVariableError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let RemoveEditVariableError::InternalSolverError(msg) = self {
+            write!(f, "internal solver error '{}'", msg)
+        } else {
+            write!(f, "{}", self.description())
+        }
+    }
+}
+
+impl Error for RemoveEditVariableError {
+    fn description(&self) -> &str {
+        match self {
+            RemoveEditVariableError::UnknownEditVariable =>
+                "variable is not marked as an edit variable",
+            RemoveEditVariableError::InternalSolverError(_) => 
+                "internal solver error",
+        }
+    }
+}
+
+/// The possible error conditions that `Solver::suggest_value` can fail with.
+#[derive(Debug, Copy, Clone)]
+pub enum SuggestValueError {
+    /// The specified variable was not an edit variable in the solver, so cannot have its value suggested.
+    UnknownEditVariable,
+    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
+    /// additional details as a string.
+    InternalSolverError(&'static str)
+}
+
+impl fmt::Display for SuggestValueError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let SuggestValueError::InternalSolverError(msg) = self {
+            write!(f, "internal solver error '{}'", msg)
+        } else {
+            write!(f, "{}", self.description())
+        }
+    }
+}
+
+impl Error for SuggestValueError {
+    fn description(&self) -> &str {
+        match self {
+            SuggestValueError::UnknownEditVariable =>
+                "variable is not marked as an edit variable",
+            SuggestValueError::InternalSolverError(_) => 
+                "internal solver error",
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub(crate) struct InternalSolverError(pub &'static str);

src/lib.rs

@@ -225,10 +225,15 @@
 //! One thing that this example exposes is that this crate is a rather low level library. It does not have
 //! any inherent knowledge of user interfaces, directions or boxes. Thus for use in a user interface this
 //! crate should ideally be wrapped by a higher level API, which is outside the scope of this crate.
+pub use error::{AddConstraintError, RemoveConstraintError, AddEditVariableError, 
+                RemoveEditVariableError, SuggestValueError};
+pub use solver_impl::Solver;
+
 use std::sync::Arc;
 use std::collections::HashMap;
 use std::collections::hash_map::{Entry};
 
+mod error;
 mod solver_impl;
 mod operators;
 
@@ -566,58 +571,4 @@ impl Row {
     }
 }
 
-/// The possible error conditions that `Solver::add_constraint` can fail with.
-#[derive(Debug, Copy, Clone)]
-pub enum AddConstraintError {
-    /// The constraint specified has already been added to the solver.
-    DuplicateConstraint,
-    /// The constraint is required, but it is unsatisfiable in conjunction with the existing constraints.
-    UnsatisfiableConstraint,
-    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
-    /// additional details as a string.
-    InternalSolverError(&'static str)
-}
-
-/// The possible error conditions that `Solver::remove_constraint` can fail with.
-#[derive(Debug, Copy, Clone)]
-pub enum RemoveConstraintError {
-    /// The constraint specified was not already in the solver, so cannot be removed.
-    UnknownConstraint,
-    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
-    /// additional details as a string.
-    InternalSolverError(&'static str)
-}
-
-/// The possible error conditions that `Solver::add_edit_variable` can fail with.
-#[derive(Debug, Copy, Clone)]
-pub enum AddEditVariableError {
-    /// The specified variable is already marked as an edit variable in the solver.
-    DuplicateEditVariable,
-    /// The specified strength was `REQUIRED`. This is illegal for edit variable strengths.
-    BadRequiredStrength
-}
 
-/// The possible error conditions that `Solver::remove_edit_variable` can fail with.
-#[derive(Debug, Copy, Clone)]
-pub enum RemoveEditVariableError {
-    /// The specified variable was not an edit variable in the solver, so cannot be removed.
-    UnknownEditVariable,
-    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
-    /// additional details as a string.
-    InternalSolverError(&'static str)
-}
-
-/// The possible error conditions that `Solver::suggest_value` can fail with.
-#[derive(Debug, Copy, Clone)]
-pub enum SuggestValueError {
-    /// The specified variable was not an edit variable in the solver, so cannot have its value suggested.
-    UnknownEditVariable,
-    /// The solver entered an invalid state. If this occurs please report the issue. This variant specifies
-    /// additional details as a string.
-    InternalSolverError(&'static str)
-}
-
-#[derive(Debug, Copy, Clone)]
-struct InternalSolverError(&'static str);
-
-pub use solver_impl::Solver;

src/solver_impl.rs

@@ -8,13 +8,13 @@ use {
     Row,
     AddConstraintError,
     RemoveConstraintError,
-    InternalSolverError,
     SuggestValueError,
     AddEditVariableError,
     RemoveEditVariableError,
     RelationalOperator,
     near_zero
 };
+use error::InternalSolverError;
 
 use ::std::rc::Rc;
 use ::std::cell::RefCell;