Rename dplyr 0.7+ function

Question

I find it hard to rename columns to functions using dplyr. I have already found useful posts about custom evaluation and use of enquo (for example, http://dplyr.tidyverse.org/articles/programming.html and Changing Result Variable Names in the dplyr Custom Function ). The ultimate goal is to use a function to summarize each group, and then rename the columns to something more meaningful than the original variable names.

Here is a simple example that works, except for the missing lines.

library(tidyverse)

myfunc <- function(df, groupvar, colvar, grouplab, collab) {
  groupvar <- enquo(groupvar)
  colvar <- enquo(colvar)
  grouplab <- enquo(grouplab)  # quo_name instead?
  collab <- enquo(collab)  # quo_name instead?

t <- df %>%
  select(!!groupvar, !!colvar) %>%
  group_by(!!groupvar, !!colvar) %>%
  summarise(
    Frequencies = length(!!colvar),
    Percentages = length(!!colvar) / nrow(df)
    ) %>%
  mutate(
    Frequencies = scales::comma(Frequencies),
    Percentages = scales::percent(Percentages)
    ) #%>%
# rename(
#    (!!grouplab) = !!groupvar,  # add a more descriptive grouping var label
#    (!!collab) = !!colvar)  # add a more descriptive column var label

# Error: unexpected '=' in: rename((!!grouplab) = "

...  # code to create an xtable, print it into LaTeX
}

myfunc <- (df = mtcars, groupvar = gear, colvar = cyl, grouplab = "Vehicle Gears", collab = "Vehicle Cylinders")
# I purposely made grouplab and collab have a space in case that changes anything. 

Outside of the functions, the corresponding part will simply read: mtcars <- mtcars %>% rename("Vehicle Cylinders" = cyl, "Vehicle Gears" = gear)

I need to understand how renaming works in a function compared to it. Any advice? I am open to suggestions.

UPDATE
. , . .

library(tidyverse)
library(xtable)
data(mtcars)

t_groupedfreqprop <- function(df, groupvar, colvar, grouplab, collab, plotname) {
groupvar2 <- rlang::sym(groupvar)
colvar2 <- rlang::sym(colvar)
grouplab <- rlang::sym(grouplab)
collab <- rlang::sym(collab)

t <- df %>%
  select(!!groupvar2, !!colvar2) %>%
  group_by(!!groupvar2, !!colvar2) %>%
  summarise(
    Frequencies = length(!!colvar2),
    Percentages = length(!!colvar2) / nrow(df)
  ) %>%
  mutate(
    Frequencies = scales::comma(Frequencies),
    Percentages = scales::percent(Percentages)
  ) %>%
  rename(
    !!grouplab := !!rlang::sym(groupvar2),
    !!collab := !!rlang::sym(colvar2)
  )

# remainder of function removed
}

t_groupedfreqprop(df = mtcars, groupvar = "gear", colvar = "cyl", grouplab = "Vehicle Gears", collab = "Vehicle Cylinders")

Answer 1

:=, LHS .

x <- "mpg"
xnew <- "mpg2"
rename(mtcars, !!xnew := !!rlang::sym(x))

Answer 2

, !!!:

x <- c("mpg", "cyl")
xnew <- paste(x, 2, sep = ".")
names(x) <- xnew
rename(mtcars, !!!x)