Polish: autobind decode method

CHANGELOG.md

@@ -14,6 +14,11 @@
 **Note**: Gaps between patch versions are faulty/broken releases. **Note**: A feature tagged as Experimental is in a
 high state of flux, you're at risk of it changing without notice.
 
+# 1.8.4
+
+- **Polish**
+  - autobind `decode` method (@gcanti)
+
 # 1.8.3
 
 - **Polish**

package.json

@@ -1,6 +1,6 @@
 {
   "name": "io-ts",
-  "version": "1.8.3",
+  "version": "1.8.4",
   "description": "TypeScript compatible runtime type system for IO validation",
   "files": [
     "lib"

src/index.ts

@@ -115,7 +115,9 @@ export class Type<A, O = A, I = unknown> implements Decoder<I, A>, Encoder<A, O>
     readonly validate: Validate<I, A>,
     /** converts a value of type A to a value of type O */
     readonly encode: Encode<A, O>
-  ) {}
+  ) {
+    this.decode = this.decode.bind(this)
+  }
 
   pipe<B, IB, A extends IB, OB extends A>(
     this: Type<A, O, I>,

test/TypeClass.ts

@@ -1,7 +1,7 @@
 import * as assert from 'assert'
 import * as t from '../src/index'
 import { assertSuccess, assertFailure } from './helpers'
-import { right } from 'fp-ts/lib/Either'
+import { right, Either } from 'fp-ts/lib/Either'
 
 const BAA = new t.Type<number, string, string>(
   'BAA',
@@ -19,6 +19,28 @@ const BAI = t.string.pipe(
 )
 
 describe('Type', () => {
+  it('should auto bind decode', () => {
+    function clone<C extends t.Any>(t: C): C {
+      const r = Object.create(Object.getPrototypeOf(t))
+      ;(Object as any).assign(r, t)
+      return r
+    }
+
+    const T = t.string
+    const decode = <L, A>(f: (u: unknown) => Either<L, A>, u: unknown): boolean => f(u).isRight()
+    assert.strictEqual(decode(T.decode, 'a'), true)
+    assert.strictEqual(decode(clone(T).decode, 'a'), true)
+    type A = {
+      a: A | null
+    }
+    const A: t.Type<A> = t.recursion('A', () =>
+      t.type({
+        a: t.union([A, t.null])
+      })
+    )
+    assert.strictEqual(decode(clone(A).decode, { a: { a: null } }), true)
+  })
+
   describe('pipe', () => {
     it('should assign a default name', () => {
       const AOI = t.string