getById.js

/* core-module/modulescommon/getById.js */


const INITIAL_STATE = {
  data: {},
  loading: false,
  error: false,
};

const REQUEST = 'BY_ID_REQUEST';
const SUCCESS = 'BY_ID_SUCCESS';
const FAILURE = 'BY_ID_FAILURE';

export const request = (prefix, params) => ({
  type: `${prefix}_${REQUEST}`,
  name: prefix,
  params,
});

export const success = prefix => ({
  type: `${prefix}_${SUCCESS}`,
});

export const failure = prefix => ({
  type: `${prefix}_${FAILURE}`,
});

export const simpleRequest = (state = INITIAL_STATE, action) => {
  switch (action.type) {
    case `${action.name}_${REQUEST}`:
      return { ...state, loading: true };
    case `${action.name}_${SUCCESS}`:
      return {
        ...state,
        data: action.data,
        loading: false,
        error: false,
      };
    case `${action.name}_${FAILURE}`:
      return { ...state, loading: false, error: true };
    default:
      return state;
  }
};

index.js

/* core-module/index.js */

import { combineReducers } from 'redux';
import createNamedWrapperReducer from 'core-module/utils/reduxUtils';
import configureStore from 'core-module/config/configureStore';
import rootSaga from 'store/sagas';

import { simpleRequest } from 'core-module/module/common/simpleRequest';
import { getById } from 'core-module/module/common/getById';

export default () => {
  const appReducer = combineReducers({
    createStock: createNamedWrapperReducer(simpleRequest, 'CREATE_STOCK'),
    getStockById: createNamedWrapperReducer(getById, 'GET_STOCK'
  });

  const rootReducer = (state, action) => appReducer(state, action);

  return configureStore(rootReducer, rootSaga);
};

reduxUtils.js

/* core-moduke/reduxUtils.js */

export function createNamedWrapperReducer(reducerFunction, reducerName) {
  return (state, action) => {
    const { name } = action;
    if (state === undefined || name === reducerName) {
      return reducerFunction(state, action);
    }

    return state;
  };
}

simpleRequest.js

/* core-module/modulescommon/simpleRequest.js */

const INITIAL_STATE = {
  loading: false,
  error: false,
};

const REQUEST = 'REQUEST';
const SUCCESS = 'SUCCESS';
const FAILURE = 'FAILURE';

export const request = (prefix, params) => ({
  type: `${prefix}_${REQUEST}`,
  name: prefix,
  params,
});

export const success = prefix => ({
  type: `${prefix}_${SUCCESS}`,
});

export const failure = prefix => ({
  type: `${prefix}_${FAILURE}`,
});

export const simpleRequest = (state = INITIAL_STATE, action) => {
  switch (action.type) {
    case `${action.name}_${REQUEST}`:
      return { ...state, loading: true };
    case `${action.name}_${SUCCESS}`:
      return { ...state, loading: false, error: false };
    case `${action.name}_${FAILURE}`:
      return { ...state, loading: false, error: true };
    default:
      return state;
  }
};

Olhei seus fontes mas não consegui assimilar direito o funcionamento, dentro da sua ideia. Mas gosto muito dessa iniciativa de enxugar e reaproveitar código. Abraços!