Add Either type

src/op.nim

@@ -25,28 +25,61 @@
 ##  assert r.isOk == false
 ##  assert r.error == "Cannot divide by zero!"
 
+import macros
+
 type
-  OP*[T] = object
-    ## Object to wrap the result of an operation.
-    ##
-    ## The type is discriminated by the `isOK` bool.
-    ## So it is an compiler error to try to access the value without checking
-    ## if the operation was successful.
-    ##
-    ## - `isOk`: Indicates if the operation was successful
-    ## - `val`: If successful, this will hold the real result value
-    ## - `error`: Otherwise this will hold an error message
-    case isOk*: bool
+  Either*[A, B] = object
+    case isA: bool
     of true:
-      val*: T
+      a: A
     of false:
-      error*: string
+      b: B
 
-proc ok*[T](val: T): OP[T] {.inline.} =
+  OP*[T] = Either[T, string]
+    ## Alias of `Either` with a string as error message
+
+
+template checkA*(self: Either): bool = self.isA
+template getA*[A, B](self: Either[A, B]): A = self.a
+template getB*[A, B](self: Either[A, B]): B = self.b
+
+proc newEitherA*[A, B](a: A): Either[A, B] {.inline.} =
+  Either[A, B](isA: true, a: a)
+
+proc newEitherB*[A, B](b: B): Either[A, B] {.inline.} =
+  Either[A, B](isA: false, b: b)
+
+template isOK*(self: OP): bool = checkA(self)
+template val*(self: OP): auto = getA(self)
+template error*(self: OP): auto = getB(self)
+
+template ok*[T](val: T): OP[T] =
   ## Wraps the given value in a successful operation result.
-  OP[T](isOK: true, val: val)
+  newEitherA[T, string](val)
 
-proc fail*(op: OP, msg: string): OP {.inline.} =
+template ok*[T](self: var OP[T], val: T) =
+  ## Set the result to the given value
+  self = ok val
+
+template fail*[T](O: type OP[T], msg: string): O =
+  ## Will create a new operation result with the given error message.
+  ## The type for the operation result is given explicitly.
+  ##
+  ## **See Also:**
+  ## - `fail proc<#fail,OP,string>`_
+  ## - `fail template<#fail.t,static[string]>`_
+  newEitherB[T, string](msg)
+
+template fail*(T: typedesc, msg: string): OP[T] =
+  ## Will create a new operation result with the given error message.
+  ## The type for the operation result is given explicitly.
+  ##
+  ## **See Also:**
+  ## - `fail proc<#fail,OP,string>`_
+  ## - `fail template<#fail.t,static[string]>`_
+  newEitherB[T, string](msg)
+
+template fail*(op: OP, msg: string): OP =
   ## Will create a new operation result with the given error message.
   ## The type for the operation result is taken from the `op` argument.
   runnableExamples:
@@ -56,19 +89,7 @@ proc fail*(op: OP, msg: string): OP {.inline.} =
     let data = someProc()
     assert data.isOk == false
     assert data.error == "Not implemented!"
-  OP(isOK: false, error: msg)
-
-proc fail*(T: typedesc, msg: string): OP[T] {.inline.} =
-  ## Will create a new operation result with the given error message.
-  ## The type for the operation result is given explicitly.
-  ##
-  ## **See Also:**
-  ## - `fail proc<#fail,OP,string>`_
-  ## - `fail template<#fail.t,static[string]>`_
-  OP[T](isOK: false, error: msg)
-
-template fail*[T](O: type OP[T], msg: string): O = O(isOK: false, error: msg)
-
-template fail*(msg: static[string]): auto = fail(typeof(result), msg)
+  fail(typeof(op), msg)
 
 
+template fail*(msg: static[string]): auto = fail(typeof(result), msg)

tests/tests.nim

@@ -4,6 +4,12 @@ import unittest
 import op
 
 suite "Basic tests":
+  proc divide(a, b: int): OP[float] =
+    if b == 0:
+      return fail "Cannot divide by zero!"
+    else:
+      return ok a / b
+
   test "Check OK":
     let test = ok 1
     check test.isOk == true
@@ -16,9 +22,9 @@ suite "Basic tests":
     proc createValue: OP[string] =
       let myString = "This is test code!"
       ok myString
-    let data = createValue()
-    check data.isOk
-    check data.val == "This is test code!"
+    let r = createValue()
+    check r.isOk
+    check r.val == "This is test code!"
 
   test "Check failing result proc":
     proc someProc(): OP[int] =
@@ -54,38 +60,53 @@ suite "Basic tests":
     check data.isOk == false
     check data.error == "data got corrupted"
 
-  test "Check divider proc":
-    proc divide(a, b: int): OP[float] =
-      if b == 0:
-        return fail(float, "Cannot divide by zero!")
-      else:
-        return ok a / b
-
-    let
-      a = 42
-      b = 0
-    let r = divide(a, b)
-    check r.isOk == false
-    check r.error == "Cannot divide by zero!"
+  test "Check divider OK":
+      let r = divide(12, 6)
+      check r.isOk == true
+      check r.val == 2
 
   test "Check implicit fail type":
-    proc divide(a, b: int): OP[float] =
-      if b == 0:
-        return fail "Cannot divide by zero!"
-      else:
-        return ok a / b
-
     let r = divide(1, 0)
     check r.isOk == false
     check r.error == "Cannot divide by zero!"
 
-  test "Check type of impolicit fail":
-      proc divide(a, b: int): OP[float] =
-        if b == 0:
-          return fail "Cannot divide by zero!"
-        else:
-          return ok a / b
+  test "Check case":
+    let r = divide(1, 2)
+    case r.isOK:
+    of true:
+      check r.val == 0.5
+    of false:
+      echo r.error
 
-      let r = divide(1, 0)
-      check r.isOk == false
-      check r.error == "Cannot divide by zero!"
+  test "Check hiding of Either":
+    let r = divide(1, 2)
+    case r.isOK:
+    of true:
+      check r.val == 0.5
+    of false:
+      echo r.error
+
+  test "Expect invalid field":
+    let r = divide(1, 2)
+    expect FieldError:
+      echo r.error
+
+  test "Expect in case":
+    let r = divide(1, 2)
+    case r.isOK:
+    of true:
+      expect FieldError:
+        echo r.error
+    of false:
+      echo r.error
+
+  # These will not work. How could this be done?
+  # test "Expect access before check":
+  #     let r = divide(1, 2)
+  #     expect FieldError:
+  #       echo r.val
+
+  # test "Expect invalid field after check":
+  #     let r = divide(1, 2)
+  #     if r.isOK:
+  #       echo r.error