add TypeOf operator to Codec, Encoder, Eq and Guard, closes #462

CHANGELOG.md

@@ -18,8 +18,14 @@
 
 - **Experimental**
   - add `Eq` module (@gcanti)
+  - `Codec`
+    - add `TypeOf` operator (@gcanti)
   - `Decoder`
     - add `DecodeError` interface (@gcanti)
+  - `Encoder`
+    - add `TypeOf` operator (@gcanti)
+  - `Guard`
+    - add `TypeOf` operator (@gcanti)
 
 # 2.2.1
 

docs/modules/Codec.ts.md

@@ -13,6 +13,7 @@ Added in v2.2.0
 <h2 class="text-delta">Table of contents</h2>
 
 - [Codec (interface)](#codec-interface)
+- [TypeOf (type alias)](#typeof-type-alias)
 - [URI (type alias)](#uri-type-alias)
 - [URI](#uri)
 - [UnknownArray](#unknownarray)
@@ -52,6 +53,16 @@ export interface Codec<A> extends D.Decoder<A>, E.Encoder<A> {}
 
 Added in v2.2.0
 
+# TypeOf (type alias)
+
+**Signature**
+
+```ts
+export type TypeOf<C> = C extends Codec<infer A> ? A : never
+```
+
+Added in v2.2.2
+
 # URI (type alias)
 
 **Signature**

docs/modules/Encoder.ts.md

@@ -13,6 +13,7 @@ Added in v2.2.0
 <h2 class="text-delta">Table of contents</h2>
 
 - [Encoder (interface)](#encoder-interface)
+- [TypeOf (type alias)](#typeof-type-alias)
 - [URI (type alias)](#uri-type-alias)
 - [URI](#uri)
 - [array](#array)
@@ -42,6 +43,16 @@ export interface Encoder<A> {
 
 Added in v2.2.0
 
+# TypeOf (type alias)
+
+**Signature**
+
+```ts
+export type TypeOf<E> = E extends Encoder<infer A> ? A : never
+```
+
+Added in v2.2.2
+
 # URI (type alias)
 
 **Signature**

docs/modules/Eq.ts.md

@@ -12,6 +12,7 @@ Added in v2.2.2
 
 <h2 class="text-delta">Table of contents</h2>
 
+- [TypeOf (type alias)](#typeof-type-alias)
 - [UnknownArray](#unknownarray)
 - [UnknownRecord](#unknownrecord)
 - [array](#array)
@@ -30,6 +31,16 @@ Added in v2.2.2
 
 ---
 
+# TypeOf (type alias)
+
+**Signature**
+
+```ts
+export type TypeOf<E> = E extends Eq<infer A> ? A : never
+```
+
+Added in v2.2.2
+
 # UnknownArray
 
 **Signature**

docs/modules/Guard.ts.md

@@ -13,6 +13,7 @@ Added in v2.2.0
 <h2 class="text-delta">Table of contents</h2>
 
 - [Guard (interface)](#guard-interface)
+- [TypeOf (type alias)](#typeof-type-alias)
 - [URI (type alias)](#uri-type-alias)
 - [URI](#uri)
 - [UnknownArray](#unknownarray)
@@ -49,6 +50,16 @@ export interface Guard<A> {
 
 Added in v2.2.0
 
+# TypeOf (type alias)
+
+**Signature**
+
+```ts
+export type TypeOf<G> = G extends Guard<infer A> ? A : never
+```
+
+Added in v2.2.2
+
 # URI (type alias)
 
 **Signature**

src/Codec.ts

@@ -20,6 +20,11 @@ import { Schemable, Literal } from './Schemable'
  */
 export interface Codec<A> extends D.Decoder<A>, E.Encoder<A> {}
 
+/**
+ * @since 2.2.2
+ */
+export type TypeOf<C> = C extends Codec<infer A> ? A : never
+
 // -------------------------------------------------------------------------------------
 // constructors
 // -------------------------------------------------------------------------------------

src/Encoder.ts

@@ -18,6 +18,11 @@ export interface Encoder<A> {
   readonly encode: (a: A) => unknown
 }
 
+/**
+ * @since 2.2.2
+ */
+export type TypeOf<E> = E extends Encoder<infer A> ? A : never
+
 // -------------------------------------------------------------------------------------
 // primitives
 // -------------------------------------------------------------------------------------

src/Eq.ts

@@ -7,6 +7,11 @@ import * as R from 'fp-ts/lib/Record'
 import * as S from './Schemable'
 import Eq = E.Eq
 
+/**
+ * @since 2.2.2
+ */
+export type TypeOf<E> = E extends Eq<infer A> ? A : never
+
 // -------------------------------------------------------------------------------------
 // primitives
 // -------------------------------------------------------------------------------------

src/Guard.ts

@@ -14,6 +14,11 @@ export interface Guard<A> {
   is: (u: unknown) => u is A
 }
 
+/**
+ * @since 2.2.2
+ */
+export type TypeOf<G> = G extends Guard<infer A> ? A : never
+
 // -------------------------------------------------------------------------------------
 // constructors
 // -------------------------------------------------------------------------------------