stampit API

stampit API

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Merging algorithm

Last updated 6 months ago
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When composing stamps you actually merge their descriptors (aka metadata).

The Object.assign is used for these descriptor properties:

The special deep merging algorithm (see below) is used for these descriptor properties:

The array concatenation and deduplication (see below) is used for these descriptor properties:

Array concatenation and deduplication

This is how initializers and composers metadata gets merged.

const _ = require('lodash')
​
descriptor.initializers = _.uniq(_.concat(descriptor1.initializers, descriptor2.initializers))
descriptor.composers = _.uniq(_.concat(descriptor1.composers, descriptor2.composers))

See the exact line of the reference implementation source code.

Deep merging algorithm

The stamp specification standardized the deep merging algorithm to, basically, this:

  • Plain objects are (recursively) deep merged, including ES6 Symbol keys.

  • Arrays are concatenated.

  • Functions, Symbols, RegExp, etc. values are copied by reference.

  • The last object type overwrites previous object type.

const MyStamp1 = stampit()
​
const deepObject1 = {
  [Symbol('foo')]: { one: 'first' },                 // this plain object will be deep merged
​
  array: [0, 'bar', () => {}, { obj: 'my object' }], // this array will be concatenated with
​
  func: MyStamp1,                                    // this stamp will be replaced with another stamp
​
  something: [42],                                   // this array will be replaced with an object
​
  oldKey: 'some value'
}
​
const MyStamp2 = stampit()
​
const deepObject2 = {
  [Symbol('foo')]: { two: 'second' },
​
  array: [0, 'bar', { another: 'object' }],
​
  func: MyStamp2,
​
  something: { [0]: 42 },
​
  newKey: 'some value'
}

The merged result of the two objects above will be this:

const deepResult = {
  [Symbol('foo')]: { one: 'first', two: 'second' }, // contains properties from both objects
​
  array: [0, 'bar', () => {}, { obj: 'my object' }, 0, 'bar', { another: 'object' }], // both arrays are here
​
  func: MyStamp2,                                   // Stamp2 replaced the Stamp1
​
  something: { [0]: 42 },                           // the array was replaced with the object
​
  oldKey: 'some value',                             // these two were simply carried across
  newKey: 'some value'
}

See the exact line of the reference implementation source code.

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