set_callback

Install a callback for the given event.

set_callback :save, :before, :before_method
set_callback :save, :after,  :after_method, if: :condition
set_callback :save, :around, ->(r, block) { stuff; result = block.call; stuff }

The second argument indicates whether the callback is to be run :before, :after, or :around the event. If omitted, :before is assumed. This means the first example above can also be written as:

set_callback :save, :before_method

The callback can be specified as a symbol naming an instance method; as a proc, lambda, or block; or as an object that responds to a certain method determined by the :scope argument to #define_callbacks.

If a proc, lambda, or block is given, its body is evaluated in the context of the current object. It can also optionally accept the current object as an argument.

Before and around callbacks are called in the order that they are set; after callbacks are called in the reverse order.

Around callbacks can access the return value from the event, if it wasn’t halted, from the yield call.

Options

• :if - A symbol or an array of symbols, each naming an instance method or a proc; the callback will be called only when they all return a true value.

  If a proc is given, its body is evaluated in the context of the current object. It can also optionally accept the current object as an argument.

• :unless - A symbol or an array of symbols, each naming an instance method or a proc; the callback will be called only when they all return a false value.

  If a proc is given, its body is evaluated in the context of the current object. It can also optionally accept the current object as an argument.

• :prepend - If true, the callback will be prepended to the existing chain rather than appended.