wrapper: Wrapper and dollar-name interceptors.

In lbartnik/ui: User Interface for Artifact Repository

Description

In order to separate the user-facing API from the testable code that implements user-facing API, all user-facing S3 classes are always wrapped in the "wrapper" class. Moreover, instead of overloading the [[ and $ operators and the .DollarNames method for all these user-facing classes, three new methods are introduced, namely: double_bracket, dollar_name and dollar_names, which have the exact same semantics. This way, in the test code, accessing actual data can be clearly distinguished from the user-facing tab-completion mechanism.

wrap puts x in a list and sets that list's class to "wrapper".

unwrap returns the original wrapped object.

print.wrapper calls the actual print method for the unwrapped object.

str.wrapper is required because RStudio calls str on objects from the global environment, whose .default version calls the [[ operator, which produces a message. This is confusing to the end user because they haven't requested an explicit object extraction.

the .DollarNames method and the $ operator are the only user-facing entry points into the tab-completion mechanism.

dollar_names is an equivalent of .DollarNames and dollar_name is an equivalent of the $ operator. All S3 classes that are publicly exposed via the "wrapper" class need to define their own version of these two methods to enable tab completion.

Usage

wrap(x, class)

unwrap(x)

is_wrapper(x)

## S3 method for class 'wrapper'
print(x, ...)

## S3 method for class 'wrapper'
str(object, ...)

## S3 method for class 'wrapper'
.DollarNames(x, pattern = "")

## S3 method for class 'wrapper'
x$i

## S3 method for class 'wrapper'
x[[i]]

dollar_names(x, pattern = "", ...)

dollar_name(x, i)

double_bracket(x, i)

## S3 method for class 'wrapper'
dollar_names(x, pattern = "", ...)

## S3 method for class 'wrapper'
dollar_name(x, i)

## S3 method for class 'wrapper'
double_bracket(x, i)

## Default S3 method:
dollar_names(x, pattern = "", ...)

## Default S3 method:
dollar_name(x, i)

Arguments

x	object to be wrapped, a wrapper object to be unwrapped or printed, or any other object to be tested.
class	optional S3 class name assigned alongside the "wrapper" class.
...	further arguments passed to or from other methods.
object	wrapper object.
pattern	regular expression; only matching names are returned.
i	key name, index value.

lbartnik/ui documentation built on May 21, 2019, 9:38 a.m.