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PSP22 Metadata

This example shows how you can reuse the implementation of PSP22 token with the PSP22Metadata extension.

Step 1: Add imports and enable unstable feature​

Use openbrush::contract macro instead of ink::contract. Import everything from openbrush::contracts::psp22::extensions::metadata.

#![cfg_attr(not(feature = "std"), no_std)]
#![feature(min_specialization)]

#[openbrush::contract]
pub mod my_psp22 {
    use openbrush::contracts::psp22::extensions::metadata::*;
    use ink_prelude::string::String;
    use ink_storage::traits::SpreadAllocate;

Step 2: Define storage​

Declare the storage struct and declare the field related to the PSP22MetadataStorage trait in addition to your PSP22Storage field. Then you need to derive the PSP22MetadataStorage trait and mark the corresponding field with the #[PSP22MetadataStorageField] attribute. Deriving this trait allows you to reuse the PSP22Metadata extension in your PSP22 implementation.

#[ink(storage)]
#[derive(Default, SpreadAllocate, PSP22Storage, PSP22MetadataStorage)]
pub struct MyPSP22 {
    #[PSP22StorageField]
    psp22: PSP22Data,
    #[PSP22MetadataStorageField]
    metadata: PSP22MetadataData,
}

Step 3: Inherit logic​

Inherit the implementation of the PSP22Metadata trait. You can customize (override) methods in this impl block.

Inherit the implementation of the PSP22 trait.

impl PSP22 for MyPSP22 {}

impl PSP22Metadata for MyPSP22 {}

Step 4: Define constructor​

Define constructor. Your PSP22Metadata contract is ready!

impl MyPSP22 {
    #[ink(constructor)]
    pub fn new(total_supply: Balance, name: Option<String>, symbol: Option<String>, decimal: u8) -> Self {
        ink_lang::codegen::initialize_contract(|instance: &mut Self| {
            instance.metadata.name = name;
            instance.metadata.symbol = symbol;
            instance.metadata.decimals = decimal;
            instance
                ._mint(instance.env().caller(), total_supply)
                .expect("Should mint total_supply");
        })
    }
}

You can check an example of the usage of PSP22 Metadata.

You can also check the documentation for the basic implementation of PSP22.