Below is my block of code where I am implementing this trait Config. I am not sure what I am doing wrong here I keep getting error "the type parameter T is not constrained by the impl trait, self type, or predicates"

pub trait Config: frame_system::Config {
    type Who;
    type RuntimeEvent;
    type OriginSuccess;
    type SchemaCreatorId;
    type MaxEncodedSchemaLength;
    type WeightInfo;
    type EnsureOrigin;
    type Origin;
impl<T: frame_system::Config> Config for Test {
    type Who = u64;
    type RuntimeEvent = Event<T>;
    type EnsureOrigin = frame_system::EnsureSignedBy<Self::Who, Self::AccountId>;
    type OriginSuccess = ();
    type SchemaCreatorId = AccountId32;
    type MaxEncodedSchemaLength = Self::MaxEncodedSchemaLength;
    type WeightInfo = Self::WeightInfo;

Attached is the screenshot of the error. unconstrained type parameter Also the codefile CodeFile If anyone can point me what I am doing wrong that would be help

2 Answers 2


that's because you are basically defining a trait that is bound by frame_system::Config, meaning the type that must implement your Config trait must also implement frame_system::Config

what you want to do is something like this:

impl my_pallet::Config for Test{...}

this will work only if Test already implements frame_system::Config (which it does in substrate https://github.com/paritytech/substrate/blob/a7bc9c2a8c0a14fd6033de1f972a11a2b3dbb73a/bin/node/runtime/src/lib.rs#L217

or for tests

https://github.com/substrate-developer-hub/substrate-node-template/blob/700c3a186e55d0d6542c564ccff17260238ed752/pallets/template/src/mock.rs#L24 )

  • Thanks this did help Commented Apr 13, 2023 at 7:29

There are a lot of examples here.


You just need impl xxx::Config for Runtime/Test { ... }.

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