Can we deploy predicates on chain?

[felix200912]

Can we deploy predicates on-chain or do we need to load each time we run it, like a script with an address and returning boolean?

[mohammadfawaz]

The following article describes predicates really well: The Power of Predicates: A Purpose-Built Mechanism for Transaction Authorization | by Ryan Sproule | Blockchain Capital Blog | Jan, 2023 | Medium

To quote the article:
“Unlike contract code, predicate code is never “deployed” to the chain. To create a predicate, someone simply writes the code for the predicate and then uses a compiler to generate a code hash, there is no interaction with the chain. Since the hash is both deterministic and collision-resistant, the coins locked in this address can only ever be spent if the predicate conditions are met. To spend a predicate, someone would provide the predicate bytecode (which must match the hash/address that the coins are behind) and a transaction that has the predicate resolve to true.”

[Daniel-Verilog]

thanks for your reply, that is a very good answer.

btw, I agree with your understanding and I personally feel predicate in sway is very similar to bitcoinscript.

However, in sway programming language github.io, there is a paragraph:

A Sway program itself has a type: it is either a contract, a predicate, a script, or a library. The first three of these things are all deployable to the blockchain. A library is simply a project designed for code reuse and is never directly deployed to the chain.

seems on the sway book, it mentions predicate is deployable.

checkout here:
https://fuellabs.github.io/sway/v0.33.1/book/sway-program-types/index.html

[mohammadfawaz]

Oh yes thank you for pointing this out. Indeed, this is a misleading sentence. We should change it, so I opened this issue: Clarify how different program types are used · Issue #3908 · FuelLabs/sway · GitHub

[Daniel-Verilog]

also checkout here:
https://fuellabs.github.io/fuel-docs/master/developer-quickstart.html

i am a bit confused here lol

[ControlCplusControlV]

Yeah fixing this now, predicates can’t be deployed, only supplied as inputs. PR for correction is open here