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x/params

Note: The Params module has been deprecated in favour of each module housing its own parameters.

Abstract​

Package params provides a globally available parameter store.

There are two main types, Keeper and Subspace. Subspace is an isolated namespace for a paramstore, where keys are prefixed by preconfigured spacename. Keeper has a permission to access all existing spaces.

Subspace can be used by the individual keepers, which need a private parameter store that the other keepers cannot modify. The params Keeper can be used to add a route to x/gov router in order to modify any parameter in case a proposal passes.

The following contents explains how to use params module for master and user modules.

Contents​

Keeper​

In the app initialization stage, subspaces can be allocated for other modules' keeper using Keeper.Subspace and are stored in Keeper.spaces. Then, those modules can have a reference to their specific parameter store through Keeper.GetSubspace.

Example:

type ExampleKeeper struct {
    paramSpace paramtypes.Subspace
}

func (k ExampleKeeper) SetParams(ctx sdk.Context, params types.Params) {
    k.paramSpace.SetParamSet(ctx, &params)
}

Subspace​

Subspace is a prefixed subspace of the parameter store. Each module which uses the parameter store will take a Subspace to isolate permission to access.

Key​

Parameter keys are human readable alphanumeric strings. A parameter for the key "ExampleParameter" is stored under []byte("SubspaceName" + "/" + "ExampleParameter"), where "SubspaceName" is the name of the subspace.

Subkeys are secondary parameter keys those are used along with a primary parameter key. Subkeys can be used for grouping or dynamic parameter key generation during runtime.

KeyTable​

All of the parameter keys that will be used should be registered at the compile time. KeyTable is essentially a map[string]attribute, where the string is a parameter key.

Currently, attribute consists of a reflect.Type, which indicates the parameter type to check that provided key and value are compatible and registered, as well as a function ValueValidatorFn to validate values.

Only primary keys have to be registered on the KeyTable. Subkeys inherit the attribute of the primary key.

ParamSet​

Modules often define parameters as a proto message. The generated struct can implement ParamSet interface to be used with the following methods:

  • KeyTable.RegisterParamSet(): registers all parameters in the struct
  • Subspace.{Get, Set}ParamSet(): Get to & Set from the struct

The implementer should be a pointer in order to use GetParamSet().