Added conversion from wasmi::Error to Option<Box<dyn HostError>> (byt…

…ecodealliance#234)

This sort of conversion is useful for extracting custom error types from the
runtime when the error type is not Clone. Even when it is, it's more
efficient to unwrap it that to clone it.

src/lib.rs

@@ -146,6 +146,11 @@ impl Trap {
     pub fn kind(&self) -> &TrapKind {
         &self.kind
     }
+
+    /// Converts into kind of this trap.
+    pub fn into_kind(self) -> TrapKind {
+        self.kind
+    }
 }
 
 impl fmt::Display for Trap {
@@ -273,7 +278,7 @@ pub enum Error {
 }
 
 impl Error {
-    /// Returns [`HostError`] if this `Error` represents some host error.
+    /// Returns a reference to a [`HostError`] if this `Error` represents some host error.
     ///
     /// I.e. if this error have variant [`Host`] or [`Trap`][`Trap`] with [host][`TrapKind::Host`] error.
     ///
@@ -282,10 +287,29 @@ impl Error {
     /// [`Trap`]: enum.Error.html#variant.Trap
     /// [`TrapKind::Host`]: enum.TrapKind.html#variant.Host
     pub fn as_host_error(&self) -> Option<&dyn host::HostError> {
-        match *self {
-            Error::Host(ref host_err) => Some(&**host_err),
-            Error::Trap(ref trap) => match *trap.kind() {
-                TrapKind::Host(ref host_err) => Some(&**host_err),
+        match self {
+            Error::Host(host_err) => Some(&**host_err),
+            Error::Trap(trap) => match trap.kind() {
+                TrapKind::Host(host_err) => Some(&**host_err),
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+
+    /// Returns [`HostError`] if this `Error` represents some host error.
+    ///
+    /// I.e. if this error have variant [`Host`] or [`Trap`][`Trap`] with [host][`TrapKind::Host`] error.
+    ///
+    /// [`HostError`]: trait.HostError.html
+    /// [`Host`]: enum.Error.html#variant.Host
+    /// [`Trap`]: enum.Error.html#variant.Trap
+    /// [`TrapKind::Host`]: enum.TrapKind.html#variant.Host
+    pub fn into_host_error(self) -> Option<Box<dyn host::HostError>> {
+        match self {
+            Error::Host(host_err) => Some(host_err),
+            Error::Trap(trap) => match trap.into_kind() {
+                TrapKind::Host(host_err) => Some(host_err),
                 _ => None,
             },
             _ => None,