Board links

Two blocks can be connected via a (directed) link. This means the result from one block is passed as (data) input to the next. Source and destination are identified by from and to attributes and in case of polyadic receiving blocks, the input attribute identified which of the data inputs is the intended destination. In principle, the link object may be extended via sub-classing and passing further attributes, but this has not been properly tested so far.

In addition to unique IDs, links objects are guaranteed to be consistent in that it is not possible to have multiple links pointing to the same target (combination of to and input attributes). Furthermore, links behave like edges in a directed acyclic graph (DAG) in that cycles are detected and disallowed.

Usage

new_link(from = "", to = "", input = "", ..., class = character())

is_link(x)

as_link(x)

links(...)

is_links(x)

as_links(x, ...)

validate_links(x)

Arguments

from, to

Block ID(s)

input

Block argument

...

Extensibility

class

(Optional) link sub-class

x

Links object

Value

Both new_link()/as_link(), and links()/as_links() return link and links objects, respectively. Testing for inheritance is available as is_link()/is_links() and validation (for links) is performed with validate_links(), which returns its input (x) or throws an error.

Details

A links is created via the new_link() constructor and for a vector of links, the container object links is provided and a corresponding constructor links() exported from the package. Testing whether an object inherits from link (or links) is available via is_link() (or is_links(), respectively). Coercion to link (and links) objects is implemented as as_link() (and as_links(), respectively). Finally, links can be validated by calling validate_links().

Examples

lnks <- links(from = c("a", "b"), to = c("b", "c"), input = c("x", "y"))
is_links(lnks)
#> [1] TRUE
names(lnks)
#> [1] "secular_nauplius" "unbiased_tarsier"

tryCatch(
  c(lnks, new_link("a", "b", "x")),
  error = function(e) conditionMessage(e)
)
#> [1] "Block b has multiple identical inputs."
tryCatch(
  c(lnks, new_link("b", "a")),
  error = function(e) conditionMessage(e)
)
#> [1] "Links form a cycle."

lnks <- links(a = new_link("a", "b"), b = new_link("b", "c"))
names(lnks)
#> [1] "a" "b"

tryCatch(
  c(lnks, a = new_link("a", "b")),
  error = function(e) conditionMessage(e)
)
#> [1] "Links IDs are required to be unique."