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Cohort hooks.

Source: R/hooks.R
hooks.Rd

In order to make integration of `cohortBuilder` package with other layers/packages easier, hooks system was introduced.

Usage

add_hook(name, method)

get_hook(name)

Arguments

name

Name of the hook. See Details section.

method

Function to be assigned as hook.

Value

No returned value (`add_hook`) or the list of functions (`get_hook`).

Details

Many Cohort methods allow to define `hook` parameter. For such method, `hook` is a list containing two values: `pre` and `post`, storing functions (hooks) executed before and after the method is run respectively.

Each `hook` is a function of two obligatory parameters:

  • public - Cohort object.

  • private - Private environment of Cohort object.

When Cohort method, for which hook is defined, allow to pass custom parameters, the ones should be also available in hook definition (with some exclusions, see below).

For example `Cohort$remove_step` has three parameters:

  • step_id

  • run_flow

  • hook

By the implementation, the parameters that we should skip are `run_flow` and `hook`, so the hook should have three parameters `public`, `private` and `step_id`.

There are two ways of defining hooks for the specific method. The first one is to define the method `hook` directly as its parameter (while calling the method).

The second option can be achieved with usage of `add_hook` (and `get_hook`) function. The default `hook` parameter for each method is constructed as below:


remove_step = function(step_id, run_flow = FALSE,
  hook = list(
    pre = get_hook("pre_rm_step_hook"),
    post = get_hook("post_rm_step_hook")
  )
)

'Pre' hooks are defined with 'pre_<method_name>_hook' and 'Post' ones as 'post_<method_name>_hook'. As a result calling:


add_hook(
  "pre_remove_step_hook",
  function(public, private, step_id) {...}
)

will result with specifying a new pre-hook for `remove_step` method.

You may add as many hooks as you want. The order of hooks execution is followed by the order or registering process. If you want to check currently registered hooks for the specific method, just use:


get_hook("pre_<method_name>_hook")