mutate create column with name from a variable - r

Question

I have a tibble data frame in R and I want to add a new column name but the name must come from the value of a variable, what is the easiest way to achieve this?
# let us generate a whole set of new features
iris_tbl = as_tibble(iris)
iris_tbl <- iris_tbl %>% mutate(hello=1)
> print(iris_tbl)
# A tibble: 150 × 6
Sepal.Length Sepal.Width Petal.Length Petal.Width Species hello
<dbl> <dbl> <dbl> <dbl> <fct> <dbl>
1 5.1 3.5 1.4 0.2 setosa 1
2 4.9 3 1.4 0.2 setosa 1
3 4.7 3.2 1.3 0.2 setosa 1
4 4.6 3.1 1.5 0.2 setosa 1
5 5 3.6 1.4 0.2 setosa 1
6 5.4 3.9 1.7 0.4 setosa 1
7 4.6 3.4 1.4 0.3 setosa 1
8 5 3.4 1.5 0.2 setosa 1
9 4.4 2.9 1.4 0.2 setosa 1
10 4.9 3.1 1.5 0.1 setosa 1
# … with 140 more rows
# ℹ Use `print(n = ...)` to see more rows
# This is the example that does not work as desired
var_name='hello'
iris_tbl = as_tibble(iris)
iris_tbl <- iris_tbl %>% mutate(var_name=1)
> print(iris_tbl)
# A tibble: 150 × 6
Sepal.Length Sepal.Width Petal.Length Petal.Width Species var_name
<dbl> <dbl> <dbl> <dbl> <fct> <dbl>
1 5.1 3.5 1.4 0.2 setosa 1
2 4.9 3 1.4 0.2 setosa 1
3 4.7 3.2 1.3 0.2 setosa 1
4 4.6 3.1 1.5 0.2 setosa 1
5 5 3.6 1.4 0.2 setosa 1
6 5.4 3.9 1.7 0.4 setosa 1
7 4.6 3.4 1.4 0.3 setosa 1
8 5 3.4 1.5 0.2 setosa 1
9 4.4 2.9 1.4 0.2 setosa 1
10 4.9 3.1 1.5 0.1 setosa 1
# … with 140 more rows
# ℹ Use `print(n = ...)` to see more rows
In the first example the column name created from mutate is actually a column called 'hello'. In the second example mutate names the column 'var_name', instead of 'hello' which is the desired outcome.
Any suggestions on how to make this as easy as possible?

Answer 1

Enter the command ?dplyr_data_masking
If you read through that, you can see there are at least 2 ways you can get your desired result.
iris_tbl <- iris_tbl %>% mutate("{var_name}" := 1)
Or
iris_tbl <- iris_tbl %>% mutate({{var_name}} := 1)