Add .toResult and .mapFailure Result extensions (#81)

* Add .toResult and .mapFailure Result extensions
block · May 21, 2024 · e3342f6 · e3342f6
1 parent c85d1bf
commit e3342f6
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diff --git a/lib/api/lib.api b/lib/api/lib.api
@@ -272,8 +272,10 @@ public final class app/cash/quiver/extensions/OptionKt {
 
 public final class app/cash/quiver/extensions/ResultKt {
 	public static final fun failure (Ljava/lang/Throwable;)Ljava/lang/Object;
+	public static final fun mapFailure (Ljava/lang/Object;Lkotlin/jvm/functions/Function1;)Ljava/lang/Object;
 	public static final fun success (Ljava/lang/Object;)Ljava/lang/Object;
 	public static final fun toEither (Ljava/lang/Object;)Larrow/core/Either;
+	public static final fun toResult (Ljava/lang/Object;Lkotlin/jvm/functions/Function0;)Ljava/lang/Object;
 }
 
 public final class app/cash/quiver/extensions/SequenceKt {

diff --git a/lib/src/main/kotlin/app/cash/quiver/extensions/Result.kt b/lib/src/main/kotlin/app/cash/quiver/extensions/Result.kt
@@ -16,3 +16,22 @@ fun <T> T.success(): Result<T> = Result.success(this)
  * Make any exception a Failure.
  */
 fun <T : Throwable> T.failure(): Result<T> = Result.failure(this)
+
+
+/**
+ * Turns a nullable value into a [Result].
+ */
+inline fun <A : Throwable, B> B?.toResult(error: () -> A): Result<B> =
+  this?.let { Result.success(it) } ?: Result.failure(error())
+
+/**
+ * If a [Result] is a failure, maps the underlying [Throwable] to a new [Throwable].
+ */
+inline fun <N : Throwable, T> Result<T>.mapFailure(
+  f: (exception: Throwable) -> N
+): Result<T> {
+  return when (val exception = exceptionOrNull()) {
+    null -> Result.success(getOrThrow())
+    else -> Result.failure(f(exception))
+  }
+}
diff --git a/lib/src/test/kotlin/app/cash/quiver/extensions/ResultTest.kt b/lib/src/test/kotlin/app/cash/quiver/extensions/ResultTest.kt
@@ -36,4 +36,15 @@ class ResultTest : StringSpec({
       it.failure() shouldBeFailure it
     }
   }
+
+  "toResult converts nullable values into Result" {
+    null.toResult { RuntimeException("boo!") }.shouldBeFailure()
+    0.toResult { RuntimeException("boo!") } shouldBeSuccess 0
+  }
+
+  "mapLeft maps the failure of a Result" {
+    val finalException = RuntimeException("Unable to map invalid integer")
+    Result.failure<Int>(NumberFormatException("Invalid integer")).mapFailure { finalException } shouldBeFailure
+      finalException
+  }
 })