Avoid implicit assignment in function calls

Assigning inside function calls makes the code difficult to read, and should be avoided, except for functions that capture side-effects (e.g. capture.output()).

Usage

implicit_assignment_linter(
  except = c("bquote", "expression", "expr", "quo", "quos", "quote"),
  allow_lazy = FALSE,
  allow_scoped = FALSE
)

Arguments

except

A character vector of functions to be excluded from linting.

allow_lazy

logical, default FALSE. If TRUE, assignments that only trigger conditionally (e.g. in the RHS of && or || expressions) are skipped.

allow_scoped

Logical, default FALSE. If TRUE, "scoped assignments", where the object is assigned in the statement beginning a branch and used only within that branch, are skipped.

See also

• linters for a complete list of linters available in lintr.

• https://style.tidyverse.org/syntax.html#assignment

Tags

best_practices, configurable, readability, style

Examples

# will produce lints
lint(
  text = "if (x <- 1L) TRUE",
  linters = implicit_assignment_linter()
)
#> ::warning file=<text>,line=1,col=5::file=<text>,line=1,col=5,[implicit_assignment_linter] Avoid implicit assignments in function calls. For example, instead of `if (x <- 1L) { ... }`, write `x <- 1L; if (x) { ... }`.

lint(
  text = "mean(x <- 1:4)",
  linters = implicit_assignment_linter()
)
#> ::warning file=<text>,line=1,col=6::file=<text>,line=1,col=6,[implicit_assignment_linter] Avoid implicit assignments in function calls. For example, instead of `if (x <- 1L) { ... }`, write `x <- 1L; if (x) { ... }`.

# okay
lines <- "x <- 1L\nif (x) TRUE"
writeLines(lines)
#> x <- 1L
#> if (x) TRUE
lint(
  text = lines,
  linters = implicit_assignment_linter()
)

lines <- "x <- 1:4\nmean(x)"
writeLines(lines)
#> x <- 1:4
#> mean(x)
lint(
  text = lines,
  linters = implicit_assignment_linter()
)

lint(
  text = "A && (B <- foo(A))",
  linters = implicit_assignment_linter(allow_lazy = TRUE)
)

lines <- c(
  "if (any(idx <- x < 0)) {",
  "  stop('negative elements: ', toString(which(idx)))",
  "}"
)
writeLines(lines)
#> if (any(idx <- x < 0)) {
#>   stop('negative elements: ', toString(which(idx)))
#> }
lint(
  text = lines,
  linters = implicit_assignment_linter(allow_scoped = TRUE)
)