Any valid symbol can be used as a keyword argument to an R function call. Sometimes, it is necessary to quote (or backtick) an argument that is not an otherwise valid symbol (e.g. creating a vector whose names have spaces); besides this edge case, quoting should not be done.
Details
The most common source of violation for this is creating named vectors, lists, or data.frame-alikes, but it can be observed in other calls as well.
Similar reasoning applies to extractions with $ or @.
See also
linters for a complete list of linters available in lintr.
Examples
# will produce lints
lint(
text = 'data.frame("a" = 1)',
linters = keyword_quote_linter()
)
#> ::warning file=<text>,line=1,col=12::file=<text>,line=1,col=12,[keyword_quote_linter] Only quote named arguments to functions if necessary, i.e., if the name is not a valid R symbol (see ?make.names).
lint(
text = "data.frame(`a` = 1)",
linters = keyword_quote_linter()
)
#> ::warning file=<text>,line=1,col=12::file=<text>,line=1,col=12,[keyword_quote_linter] Only quote named arguments to functions if necessary, i.e., if the name is not a valid R symbol (see ?make.names).
lint(
text = 'my_list$"key"',
linters = keyword_quote_linter()
)
#> ::warning file=<text>,line=1,col=9::file=<text>,line=1,col=9,[keyword_quote_linter] Only quote targets of extraction with $ if necessary, i.e., if the name is not a valid R symbol (see ?make.names). Use backticks to create non-syntactic names, or use [[ to extract by string.
lint(
text = 's4obj@"key"',
linters = keyword_quote_linter()
)
#> ::warning file=<text>,line=1,col=7::file=<text>,line=1,col=7,[keyword_quote_linter] Only quote targets of extraction with @ if necessary, i.e., if the name is not a valid R symbol (see ?make.names). Use backticks to create non-syntactic names, or use slot() to extract by string.
# okay
lint(
text = "data.frame(`a b` = 1)",
linters = keyword_quote_linter()
)
lint(
text = "my_list$`a b`",
linters = keyword_quote_linter()
)