Routers and Selectors. Part 3 match

[emil14]

Previous parts:

• if Routers and Selectors. Part 1 if #802
• switch Routers and Selectors. Part 2 switch #804

Match

Basic

Match is a selector. It selects a message to send, but not the direction, so it has only one output port connected to its body.

data_sender -> match {
    cond_sender1: then_sender1
    cond_sender2: then_sender2
    ...
    _: default_sender
} -> receiver

Example

:number -> match {
    0: zero_string    // node that sends string
    1: one_string     // another node that sends string
    ...
    _: unknown_string // and one more string node
} -> :string

One might think that dictionary data type can handle this use-case. That's not entirely true because dictionary can't have network senders as keys and values

With Multiple Conditions On a Same Branch

Similar to if, match supports multiple condition senders on a single branch. Each condition sender is compared to the incoming data message in sequence before moving to the next branch. And of course it supports multiple receivers as a fan-out.

sender -> match {
    [cond_sender1, cond_sender2]: then_sender1
    ...
} -> [receiver1, receiver1]

Example

:binary -> match {
    [0, 1]: 'valid'
    _: 'not so valid'
} -> [log, db]

Match is blocked by its data sender, its branch then_senders and its receiver. The more parts it have the more it latency can be

As a Ternary

In the same way that switch can emulate if, match can emulate the ternary operator.

sender -> match {
    true: then_sender
    _: else_sender
} -> receiver

The ternary expression should be preferred whenever possible.