cosmos-sdk/docs/spec/params/01_keeper.md

Keeper

In the app initialization stage, Keeper.Subspace(Paramspace) is passed to the user modules, and the subspaces are stored in Keeper.spaces. Later it can be retrieved with Keeper.GetSubspace, so the keepers holding Keeper can access to any subspace. For example, Gov module can take Keeper as its argument and modify parameter of any subspace when a ParameterChangeProposal is accepted.

Example:

type MasterKeeper struct {
	pk params.Keeper
}

func (k MasterKeeper) SetParam(ctx sdk.Context, space string, key string, param interface{}) {
	space, ok := k.ps.GetSubspace(space)
	if !ok {
		return
	}
	space.Set(ctx, key, param)
}