Smart Contract Overview

Overview of equity contract

Equity is a high-level language used by bytom to express contract programs. It is mainly used to describe specific assets on the bytom blockchain:

• All on-chain assets are locked in the contract program. Once the asset value (ie UTXO) is unlocked by a contract, it is only meant to be locked by one or more other contracts.
• The way that the contract protects the asset value (that is, UTXO) is that the transaction must meet the condition through the “verify” command executed through virtual machine.

Components of contract

contract ContractName ( parameters ) locks value { clauses }

• ContractName contract name is defined by user
• parameters list of contract parameters, which must conform to the basic type of contract language
• value The value of the asset (ie UTXO's asset type and corresponding value), which can be customized by the user.
• clauses (ie, functions) (one or more)

Component of Clause (function)

clause ClauseName ( parameters ) { statements }

or

clause ClauseName ( parameters ) requires name : amount of asset { statements }

• ClauseName name of clauses, which is defined by users
• parameters list of clause / function parameter
• payments other restrictions that are required to spend UTXO. For example, when performing coin-to-coin transaction, it is necessary to verify that the counterparty of the transaction can provide a corresponding asset value. The major use case of such constraints are contract trading between different types of assets.

Component of Statement

statements contract language，Only verify、lock and unlock

• the verify statement: for example verify expression，in which the result of expression must be bool type and true to continue execution
• the unlock statement: for exampleunlock value，in which value represents the value of corresponding asset
• the lock statement: for examplelock value with program，in which valuerepresents the value of corresponding asset, and program must be the program basic type.

Categories of contract: (Time type is temporarily disabled) Amount Asset Boolean Hash Integer Program PublicKey Signature String

Built-in functions: (The built-in functions related to timing “before” and “after” are temporarily disabled, the alternative is to verify the block height functions “below” and “above”)

• abs(n) returns the absolute value of the value n.
• min(x, y) returns the smallest of the two values ​​x and y.
• max(x, y) returns the largest of the two values ​​x and y.
• size(s) returns the size of any type of byte.
• concat(s1, s2) returns the string generated from connecting the two strings s1 and s2
• concatpush(s1, s2) concatenates two string-type virtual machine execution opcodes s1 and s2 (ie s2 is joined ​​behind s1) and pushes them onto the stack. The operation function is mainly used for nested contracts.
• below(height) Determines whether the current block height is lower than the parameter height, and returns true if it is, otherwise returns false.
• above(height) Determines whether the current block height is higher than the parameter height, and returns true if it is, otherwise returns false.
• sha3(s) returns the hashing result of byte type string parameter s via SHA3-256.
• sha256(s) returns the hashing result of byte type string parameter s via SHA-256
• checkTxSig(key, sig) verifies whether the multi-signature of the transaction is correct based on one PublicKey and one Signature.
• checkTxMultiSig([key1, key2, ...], [sig1, sig2, ...]) Verify that the multi-signature of the transaction is correct based on multiple PublicKeys and multiple Signatures.