Add getOrThrow

Closes #68

kotlin-result/src/commonMain/kotlin/com/github/michaelbull/result/Get.kt

@@ -121,6 +121,39 @@ public inline infix fun <V, E> Result<V, E>.getErrorOrElse(transform: (V) -> E):
     }
 }
 
+/**
+ * Returns the [value][Ok.value] if this [Result] is [Ok], otherwise throws the
+ * [error][Err.error].
+ *
+ * This is functionally equivalent to [`getOrElse { throw it }`][getOrElse].
+ */
+public fun <V, E : Throwable> Result<V, E>.getOrThrow(): V {
+    contract {
+        returns() implies (this@getOrThrow is Ok<V>)
+    }
+
+    return when (this) {
+        is Ok -> value
+        is Err -> throw error
+    }
+}
+
+/**
+ * Returns the [value][Ok.value] if this [Result] is [Ok], otherwise throws the
+ * [transformation][transform] of the [error][Err.error] to a [Throwable].
+ */
+public inline infix fun <V, E> Result<V, E>.getOrThrow(transform: (E) -> Throwable): V {
+    contract {
+        returns() implies (this@getOrThrow is Ok<V>)
+        callsInPlace(transform, InvocationKind.AT_MOST_ONCE)
+    }
+
+    return when (this) {
+        is Ok -> value
+        is Err -> throw transform(error)
+    }
+}
+
 /**
  * Merges this [Result<V, E>][Result] to [U], returning the [value][Ok.value] if this [Result] is [Ok], otherwise the
  * [error][Err.error].

kotlin-result/src/commonTest/kotlin/com/github/michaelbull/result/GetTest.kt

@@ -2,6 +2,7 @@ package com.github.michaelbull.result
 
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
 import kotlin.test.assertNull
 
 @Suppress("IMPLICIT_NOTHING_TYPE_ARGUMENT_IN_RETURN_POSITION")
@@ -54,6 +55,44 @@ class GetTest {
         }
     }
 
+    class GetOrThrow {
+        @Test
+        fun returnsValueIfOk() {
+            assertEquals(
+                expected = "hello",
+                actual = Ok("hello").getOrThrow()
+            )
+        }
+
+        @Test
+        fun throwsErrorIfErr() {
+            assertFailsWith<CustomException> {
+                Err(CustomException()).getOrThrow()
+            }
+        }
+
+        class CustomException : Throwable()
+    }
+
+    class GetOrThrowWithTransform {
+        @Test
+        fun returnsValueIfOk() {
+            assertEquals(
+                expected = "hello",
+                actual = Ok("hello").getOrThrow { CustomException("Failed") }
+            )
+        }
+
+        @Test
+        fun throwsTransformedErrorIfErr() {
+            assertFailsWith<CustomException> {
+                Err("error").getOrThrow { error -> CustomException(error) }
+            }
+        }
+
+        class CustomException(message: String) : Throwable(message)
+    }
+
     class GetErrorOr {
         @Test
         fun returnsDefaultValueIfOk() {