Typed Settings For One Pipeline Stage

The virtual base of pecotmr's *Param() records – CredibleSetParam, SusieRssParam, PanelFilterParam and the rest. Each one holds settings pecotmr itself reads, declared as typed slots and checked when the record is built.

This is the counterpart to MethodOptions, which carries arguments bound for an external engine. The distinction is deliberate and visible in the name: a *Param() is a pecotmr setting whose meaning and type pecotmr defines, so pecotmr validates it; a *Options() is somebody else's argument list, so pecotmr checks only that each name exists in that engine's live formals and otherwise does not attempt to mirror its semantics.

Usage

# S4 method for class 'MethodParam'
x$name

# S4 method for class 'MethodParam,ANY,ANY'
x[[i, j, ...]]

# S4 method for class 'MethodParam'
names(x)

# S4 method for class 'MethodParam'
length(x)

# S4 method for class 'MethodParam'
as.list(x, ...)

# S4 method for class 'MethodParam'
show(object)

Arguments

x

A MethodParam object.

name

The name of a setting.

i

A setting's name, or its position among the settings that are set.

j

Unused, for consistency with the generic.

...

Unused, for consistency with the generic.

object

A MethodParam object.

Value

$ returns that setting's value, NULL when it is unset.

[[ returns that setting's value.

names returns the settings that are set.

length returns how many settings are set.

as.list returns the settings that are set, as a named list.

show is called for its side effect and returns invisible(NULL).

List interface

A MethodParam reads like a list: $ and [[ fetch a field, and names(), length() and as.list() describe it.

Those last three report only the fields that are set. A slot holding NULL is absent from all three, while $ and [[ still return NULL for it. This is not cosmetic: as.list() on one of these records is spliced into an engine call, and an engine that distinguishes an explicit NULL argument from an omitted one would otherwise see a different call.

Unlike a list, $ on a name that is not a field is an error rather than NULL. Silently reading a misspelled setting as "unset" is the failure these classes exist to prevent.