R Programming: Object of Type 'Closure' is Not Subsettable

The error message "Object of Type 'Closure' is Not Subsettable" has presumably troubled many R users, not only beginners, and can be considered one of the less helpful messages. Here we'll answer two questions:
- How can this error come about (and how to solve it, of course)?
- What is a closure, anyway?
We'll see two ways how this error may be triggered:
1. Accidentally using [] instead of ()
2. Accidentally accessing a non-existing object that happens to be a function
In the video, I mentioned Hadley Wickham's "Advanced R" book where you can find out more about environments and namespaces:
adv-r.hadley.nz/
I also mentioned Jenny Bryan's great talk "Object of type ‘closure’ is not subsettable":
• Jenny Bryan | Object o...
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[@adamatomic41]

Thank you! I looked all over to try to fix this problem and this is the only thing that helped.

[@RochelleMphetlhe-bs6hk]

the second example helped with my problems, thank you so much

[@colbykresge960]

install.packages("foieGras", depedencies = c("Imports","LinkingTo","Suggests"))
install.packages("TMB")
library(glmmTMB)
library(foieGras)
library(foieGras)
library(readr)
HP

[@StatistikinDD]

Sorry, I have no experience using these packages and this fit function.