fix(*): remove self-types from interfaces

This patches 7a63ffe
In Typescript 2.5, some changes were made that broke checking self-types
in interfaces.  This is unfortunate in that it widens the `getOrElse`
and `orElse` interface, but does unbreak Monapt on 2.5+.

Pull requests to fix this welcome!

Fixes #20

src/option/none.ts

@@ -47,7 +47,7 @@ class None_<A> implements Option<A> {
     throw new Option.NoSuchElementError();
   }
 
-  getOrElse<B, A extends B>(this: Option<A>, defaultValue: () => B): B {
+  getOrElse<B, A extends B>(this: None_<A>, defaultValue: () => B): B {
     return defaultValue();
   }
 
@@ -59,7 +59,7 @@ class None_<A> implements Option<A> {
     return matcher.None();
   }
 
-  orElse<B, A extends B>(this: Option<A>, alternative: () => Option<B>): Option<B> {
+  orElse<B, A extends B>(this: None_<A>, alternative: () => Option<B>): Option<B> {
     return alternative();
   }
 }

src/option/option.ts

@@ -4,6 +4,8 @@ import { Some } from './some';
 /**
  * An Option represents a collection of size 0 or 1.  Traditionally it's used as a replacement for
  * `null` or `undefined` to explicitly encode if a value can be empty or not.
+ *
+ * :TODO: Narrow self-type in `getOrElse` and `orElse` interfaces.
  */
 interface Option<A> {
   isDefined: boolean;
@@ -15,10 +17,10 @@ interface Option<A> {
   flatMap<B>(flatMapper: (value: A) => Option<B>): Option<B>;
   foreach(run: (value: A) => void): void;
   get(): A;
-  getOrElse<B, A extends B>(this: Option<A>, defaultValue: () => B): B;
+  getOrElse<B>(defaultValue: () => B): B;
   map<B>(mapper: (value: A) => B): Option<B>;
   match<B>(matcher: { Some: (a: A) => B, None: () => B }): B;
-  orElse<B, A extends B>(this: Option<A>, alternative: () => Option<B>): Option<B>;
+  orElse<B>(alternative: () => Option<B>): Option<B>;
 }
 
 /* tslint:disable:no-null-keyword only-arrow-functions */

src/option/some.ts

@@ -53,10 +53,8 @@ class Some<A> implements Option<A> {
     return this.value;
   }
 
-  getOrElse<B, A extends B>(this: Option<A>, defaultValue: () => B): B {
-    const self: Some<A> = this as Some<A>;
-
-    return self.value;
+  getOrElse<B, A extends B>(this: Some<A>, defaultValue: () => B): B {
+    return this.value;
   }
 
   map<B>(mapper: (value: A) => B): Option<B> {
@@ -67,10 +65,8 @@ class Some<A> implements Option<A> {
     return matcher.Some(this.value);
   }
 
-  orElse<B, A extends B>(this: Option<A>, alternative: () => Option<B>): Option<B> {
-    const self: Some<A> = this as Some<A>;
-
-    return self;
+  orElse<B, A extends B>(this: Some<A>, alternative: () => Option<B>): Option<B> {
+    return this;
   }
 }
 

src/try/failure.ts

@@ -45,7 +45,7 @@ class Failure<A> implements Try<A> {
     throw this.error;
   }
 
-  getOrElse<B, A extends B>(this: Try<A>, defaultValue: () => B): B {
+  getOrElse<B, A extends B>(this: Failure<A>, defaultValue: () => B): B {
     return defaultValue();
   }
 
@@ -57,7 +57,7 @@ class Failure<A> implements Try<A> {
     return matcher.Failure(this.error);
   }
 
-  orElse<B, A extends B>(this: Try<A>, alternative: () => Try<B>): Try<B> {
+  orElse<B, A extends B>(this: Failure<A>, alternative: () => Try<B>): Try<B> {
     return alternative();
   }
 

src/try/success.ts

@@ -46,10 +46,8 @@ class Success<A> implements Try<A> {
     return this.value;
   }
 
-  getOrElse<B, A extends B>(this: Try<A>, defaultValue: () => B): B {
-    const self: Success<A> = this as Success<A>;
-
-    return self.value;
+  getOrElse<B, A extends B>(this: Success<A>, defaultValue: () => B): B {
+    return this.value;
   }
 
   map<B>(f: (value: A) => B): Try<B> {
@@ -60,10 +58,8 @@ class Success<A> implements Try<A> {
     return matcher.Success(this.value);
   }
 
-  orElse<B, A extends B>(this: Try<A>, alternative: () => Try<B>): Try<B> {
-    const self: Success<A> = this as Success<A>;
-
-    return self;
+  orElse<B, A extends B>(this: Success<A>, alternative: () => Try<B>): Try<B> {
+    return this;
   }
 
   recover(fn: (error: Error) => A): Try<A> {

src/try/try.ts

@@ -4,6 +4,8 @@ import { Success } from './success';
 
 /**
  * A Try represents a computation that may or may not have succeeded.
+ *
+ * :TODO: Narrow self-type in `getOrElse` and `orElse` interfaces.
  */
 interface Try<A> {
   isFailure: boolean;
@@ -13,10 +15,10 @@ interface Try<A> {
   flatMap<B>(f: (value: A) => Try<B>): Try<B>;
   foreach(run: (value: A) => void): void;
   get(): A;
-  getOrElse<B, A extends B>(this: Try<A>, defaultValue: () => B): B;
+  getOrElse<B>(defaultValue: () => B): B;
   map<B>(f: (value: A) => B): Try<B>;
   match<B>(matcher: { Success: (a: A) => B, Failure: (e: Error) => B }): B;
-  orElse<B, A extends B>(this: Try<A>, alternative: () => Try<B>): Try<B>;
+  orElse<B>(alternative: () => Try<B>): Try<B>;
   recover(fn: (error: Error) => A): Try<A>;
   recoverWith(fn: (error: Error) => Try<A>): Try<A>;
   toOption(): Option<A>;