Bird 15D5

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  "map_content": "# Buyable / Sellable Scrypt Objects\n\n## A simple pattern to \u201cmixin\u201d to any stateful smart object you want to be sellable\nIf a smart contract has an owner property and can be \"ownable\", what makes it \"sellable\"?\n\nAny contract that adds an owner property may also add a price property that indicates that the object becomes \"sellable\". It must then implement a buy() method which assigns the owner to the new owner\u2019s address only if the price is paid. It will also need a setPrice(signature: Signature) method allowing the owner to set the price. Perhaps setting the price to 0 would disallow sales, or perhaps there is another prop called buyable and a method called setBuyable(buyable: boolean) which would allow the user to list it for sale any time.\n\n```\nimport {\n    method,\n    prop,\n    SmartContract,\n    hash256,\n    hash160,\n    assert,\n    ByteString,\n    SigHash,\n    PubKey,\n    PubKeyHash,\n    Sig\n} from 'scrypt-ts'\n\nexport class Sellable extends SmartContract {\n\n    @prop(true)\n    pubKeyHash: PubKeyHash\n\n    @prop(true)\n    price: bigint\n\n    @prop(true)\n    buyable: boolean\n\n    constructor(pubKeyHash: PubKeyHash) {\n        super(...arguments)\n        this.pubKeyHash = pubKeyHash\n        this.matureTime = matureTime\n    }\n\n    // callable only by the seller\n    @method()\n    public setPrice(price: bigint, signature: Sig, pubkey: PubKey) {\n      assert(hash160(pubkey) === this.pubKeyHash)\n      assert(this.checkSig(signature, pubkey), `checkSig failed, pubKeyHash: ${this.pubKeyHash}`)\n\n      const stateOutput = this.buildStateOutput(amount)\n      assert(this.ctx.hashOutputs == hash256(stateOutput), \"Output hashes don't match\")\n\n      this.price = price;\n    }\n\n    // callable only by the seller\n    @method()\n    public setBuyable(buyable: boolean, signature: Sig, pubkey: PubKey) {\n      assert(hash160(pubkey) === this.pubKeyHash)\n      assert(this.checkSig(signature, pubkey), `checkSig failed, pubKeyHash: ${this.pubKeyHash}`)\n\n      // Could this somehow be exacted into a re-usable library like so:??\n      // import assertState from 'scrypt-assert-state'\n      // assertState(this)\n      assert(this.ctx.hashOutputs == hash256(this.buildStateOutput(this.ctx.utxo.value)), \"Output hashes don't match\")\n\n      this.buyable = buyable;\n    }\n\n    // callable only by the buyer\n    @method()\n    public buy(pubKeyHash: PubKeyHash) {\n\n     assert(this.buyable)\n\n     // Ensure exact payment of the price to the current owner's address\n     const paymentOutput = Utils.buildPublicKeyHashOutput(this.pubKeyHash, this.price)\n     assert(hash256(paymentOutput) == this.ctx.hashOutputs,  'invalid output for payment to seller')\n\n     // Ensure the smart object's state remains entirely intact during the sale\n     const stateOutput = this.buildStateOutput(this.ctx.utxo.value)\n     assert(this.ctx.hashOutputs == hash256(stateOutput), \"Output hashes don't match\")\n\n     // \"transfer\" ownership by assigning a new owner\n     this.pubKeyHash = pubKeyHash\n    }\n\n}\n```",
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  "author": "15D5UryaVwjg2ATtLVYm5854RCM2aZL8At",
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  "timestamp": "2023-07-19T19:56:02.000Z",
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