Instantiating predicates

A predicate in Sway can be as simple as the following:

<<< @/../../docs/sway/return-true-predicate/src/main.sw#predicate-simple-1{rust:line-numbers}

In this minimal example, the main function does not accept any parameters and simply returns true.

Just like contracts in Sway, once you've created a predicate, you can compile it using forc build. For more information on working with Sway, refer to the <a :href="introUrl" target="_blank" rel="noreferrer">Sway documentation</a>.

After compiling, you will obtain the binary of the predicate and its JSON ABI (Application Binary Interface). Using these, you can instantiate a predicate in TypeScript as shown in the code snippet below:

<<< @./snippets/instantiation/simple.ts#predicate-simple-2{ts:line-numbers}

The created Predicate instance, among other things, has three important properties: the predicate bytes (byte code), the chainId, and the predicate address.

This address, generated from the byte code, corresponds to the Pay-to-Script-Hash (P2SH) address used in Bitcoin.

Predicate with multiple arguments

You can pass more than one argument to a predicate. For example, this is a predicate that evaluates to true if the two arguments are not equal:

<<< @/../../docs/sway/predicate-multi-args/src/main.sw#predicate-multi-args-1{rust:line-numbers}

You can pass the two arguments to this predicate like this:

<<< @./snippets/instantiation/multi-args.ts#predicate-multi-args-2{rust:line-numbers}

Predicate with a Struct argument

You can also pass a struct as an argument to a predicate. This is one such predicate that expects a struct as an argument:

<<< @/../../docs/sway/predicate-main-args-struct/src/main.sw#predicate-main-args-struct-1{rust:line-numbers}

You can pass a struct as an argument to this predicate like this:

<<< @./snippets/instantiation/struct-arg.ts#predicate-main-args-struct-2{ts:line-numbers}