result: expose value/error in errorOr/valueOr

* fix error type as well

stew/results.nim

@@ -815,15 +815,21 @@ template valueOr*[T: not void, E](self: Result[T, E], def: untyped): T =
   ## ```
   let s = (self) # TODO avoid copy
   if s.o: s.v
-  else: def
+  else:
+    when E isnot void:
+      template error: E {.used, inject.} = s.e
+    def
 
-template errorOr*[T: not void, E](self: Result[T, E], def: untyped): E =
+template errorOr*[T, E: not void](self: Result[T, E], def: untyped): E =
   ## Fetch error of result if not set, or evaluate `def`
   ## `def` is evaluated lazily, and must be an expression of `T` or exit
   ## the scope (for example using `return` / `raise`)
   let s = (self) # TODO avoid copy
   if not s.o: s.e
-  else: def
+  else:
+    when T isnot void:
+      template value: T {.used, inject.} = s.v
+    def
 
 func flatten*[T, E](self: Result[Result[T, E], E]): Result[T, E] =
   ## Remove one level of nesting

tests/test_results.nim

@@ -69,11 +69,13 @@ block:
   doAssert rOk.get() == rOk.unsafeGet()
 
   doAssert rOk.valueOr(failFast()) == rOk.value()
-  let rErrV = rErr.valueOr: 100
-  doAssert rErrV == 100
+  let rErrV = rErr.valueOr:
+    error.len
+  doAssert rErrV == rErr.error.len()
 
-  let rOkV = rOk.errorOr: "quack"
-  doAssert rOkV == "quack"
+  let rOkV = rOk.errorOr:
+    $value
+  doAssert rOkV == $rOk.get()
 
   # Exceptions -> results
   func raises(): int =