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https://github.com/tjjfvi/subshape

composable shapes for cohesive code
https://github.com/tjjfvi/subshape

deno reflection serialization substrate typescript typing validation

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composable shapes for cohesive code

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# subShape  composable shapes for cohesive code



> ### *one shape can do them all; one shape defined them*



subShape provides primitives and patterns for crafting composable shapes

featuring cohesive typing, validation, serialization, and reflection.



## Setup



### Deno



```ts

import * as $ from "https://deno.land/x/subshape/mod.ts"

```



### Node



```

npm install subshape

```



```ts

import * as $ from "subshape"

```



## Demo



### Craft a Composable Shape



```ts

import * as $ from "https://deno.land/x/subshape/mod.ts"



const $superhero = $.object(

  $.field("pseudonym", $.str),

  $.optionalField("secretIdentity", $.str),

  $.field("superpowers", $.array($.str)),

)

```



### And Get...



#### Typing



```ts

type Superhero = $.Output

// type Superhero = {

//   pseudonym: string;

//   secretIdentity?: string | undefined;

//   superpowers: string[];

// }

```



#### Validation



```ts

const spiderMan = {

  pseudonym: "Spider-Man",

  secretIdentity: "Peter Parker",

  superpowers: ["does whatever a spider can"],

}



$.assert($superhero, spiderMan) // ok!



const bob = {

  pseudonym: "Bob",

  secretIdentity: "Robert",

  superpowers: null,

}



$.assert($superhero, bob) // ShapeAssertError: !(value.superpowers instanceof Array)

```



#### Serialization



```ts

const encoded = $superhero.encode(spiderMan)

// encoded: Uint8Array



const decoded = $superhero.decode(encoded)

// decoded: Superhero



console.log(decoded)

// Prints:

//   {

//     pseudonym: "Spider-Man",

//     secretIdentity: "Peter Parker",

//     superpowers: [ "does whatever a spider can" ]

//   }

```



#### Reflection



```ts

$superhero.metadata // Metadata



console.log($superhero)

// Prints:

//   $.object(

//     $.field("pseudonym", $.str),

//     $.optionalField("secretIdentity", $.str),

//     $.field("superpowers", $.array($.str))

//   )

```



## Examples



Further examples can be found in the

[`examples`](https://github.com/paritytech/scale-ts/tree/main/examples)

directory.



## Shape Naming Convention



This library adopts a convention of denoting shapes with a `$` – `$.foo` for

built-in shapes, and `$foo` for user-defined shapes. This makes shapes easily

distinguishable from other values, and makes it easier to have shapes in scope

with other variables:



```ts

interface Person { ... }

const $person = $.object(...)

const person = { ... }

```



Here, the type, shape, and a value can all coexist without clashing, without

having to resort to wordy workarounds like `personShape`.



The main other library this could possibly clash with is jQuery, and its usage

has waned enough that this is not a serious problem.



While we recommend following this convention for consistency, you can, of

course, adopt an alternative convention if the `$` is problematic – `$.foo` can

easily become `s.foo` or `subshape.foo` with an alternate import name.



## Asynchronous Encoding



Some shapes require asynchronous encoding. Calling `.encode()` on a shape will

throw if it or another shape it calls is asynchronous. In this case, you must

call `.encodeAsync()` instead, which returns a `Promise`. You can

call `.encodeAsync()` on any shape; if it is a synchronous shape, it will simply

resolve immediately.



Asynchronous decoding is not supported.



## Custom Shapes



If your encoding/decoding logic is more complicated, you can create custom

shapes with `createShape`:



```ts

const $foo = $.createShape({

  metadata: $.metadata("$foo"),



  // A static estimation of the encoded size, in bytes.

  // This can be either an under- or over- estimate.

  staticSize: 123,

  subEncode(buffer, value) {

    // Encode `value` into `buffer.array`, starting at `buffer.index`.

    // A `DataView` is also supplied as `buffer.view`.

    // At first, you may only write at most as many bytes as `staticSize`.

    // After you write bytes, you must update `buffer.index` to be the first unwritten byte.



    // If you need to write more bytes, call `buffer.pushAlloc(size)`.

    // If you do this, you can then write at most `size` bytes,

    // and then you must call `buffer.popAlloc()`.



    // You can also call `buffer.insertArray()` to insert an array without consuming any bytes.



    // You can delegate to another shape by calling `$bar.subEncode(buffer, bar)`.

    // Before doing so, you must ensure that `$bar.staticSize` bytes are free,

    // either by including it in `staticSize` or by calling `buffer.pushAlloc()`.

    // Note that you should use `subEncode` and not `encode`.



    // See the `EncodeBuffer` class for information on other methods.



    // ...

  },



  subDecode(buffer) {

    // Decode `value` from `buffer.array`, starting at `buffer.index`.

    // A `DataView` is also supplied as `buffer.view`.

    // After you read bytes, you must update `buffer.index` to be the first unread byte.



    // You can delegate to another shape by calling `$bar.subDecode(buffer)`.

    // Note that you should use `subDecode` and not `decode`.



    // ...

    return value

  },



  subAssert(assert) {

    // Validate that `assert.value` is valid for this shape.

    // `assert` exposes various utility methods, such as `assert.instanceof`.

    // See the `AssertState` class for information on other methods.



    // You can delegate to another shape by calling `$bar.subAssert(assert)` or `$bar.subAssert(assert.access("key"))`.

    // Any errors thrown should be an instance of `$.ShapeAssertError`, and should use `assert.path`.



    // ...

  },

})

```