.env pronouns make it explicit where to look up attribute
names when indexing
E(g), i.e. the vertex or edge sequence of a
graph. These pronouns are inspired by
rlang - thanks
to Michał Bojanowski for bringing these to our attention.
The rules are simple:
.dataretrieves attributes from the graph whose vertex or edge sequence is being evaluated.
.envretrieves variables from the calling environment.
.env are injected dynamically into the environment
where the indexing expressions are evaluated; you cannot get access to these
objects outside the context of an indexing expression. To avoid warnings
R CMD check when code containing
.env is checked,
you can import
igraph if needed. Alternatively,
you can declare them explicitly with
utils::globalVariables() to silence