问题
I'm trying to create a dynamic UI, so i used this code
output$col <- renderUI({
map(col_names(), ~ textInput(.x, NULL, value = isolate(input[[.x]])) %||% "")
})
from :
https://mastering-shiny.org/action-dynamic.html#multiple-controls
My question is basically, what is meaning of the syntax %||% ?
回答1:
The help page of sheds light into it:
?rlang::`%||%`
Description
This infix function makes it easy to replace NULLs with a default value.
It's inspired by the way that Ruby's or operation (||) works.
Usage
x %||% y
Arguments
x, y
If x is NULL, will return y; otherwise returns x.
It is similar to a coalesce function. Basically, whenever the input is NULL, that means it is not (yet) available, an empty tring is assigned rather than NULL. This is desireable because this is rendered and displayed as an empty value should. NULL would be shown like an error massage
回答2:
The %||% comes from rlang. You can find it on the ?"op-null-default" help page. From the documentation
This infix function makes it easy to replace NULLs with a default value. It's inspired by the way that Ruby's or operation (||) works.
Basically it returns the second value if the first is NULL.
来源：https://stackoverflow.com/questions/60418258/what-is-meaning-of-the-syntax