Built-in helpers for a placeholder's plain-R evaluation slot

A placeholder-embellished ggplot expression must stay valid plain R that renders the original plot with no app running. Each placeholder carries a callable (the embellish_eval = argument of the ptr_define_placeholder_*() constructors) that supplies its plain-R meaning when the naked expression is evaluated outside ptr_app(). These two factories are the built-in callables for that slot:

Usage

embellish_identity()

embellish_symbol_to_string()

Value

Each factory returns a function of signature function(x, ...). embellish_identity()'s function returns its first argument x unchanged. embellish_symbol_to_string()'s function returns a character vector of column names captured from the unevaluated x.

Details

• embellish_identity() returns the identity function(x, ...) x — the slot's default behaviour. The placeholder call becomes a no-op wrapper: it returns its argument unchanged.

• embellish_symbol_to_string() returns a function that captures its argument unevaluated and turns column references into a character vector of names. This is the pattern a column-selecting consumer needs so the naked expression works inside a tidyselect verb: tidyselect evaluates an unknown wrapper call in non-masked scope, where bare column symbols throw "object not found"; returning the names as strings sidesteps that because tidyselect accepts selection by name.

These helpers are author-controlled plain-R semantics, never derived — only the author knows the intended live-R meaning of a placeholder.

Examples

f <- embellish_identity()
f(5L)
#> [1] 5

g <- embellish_symbol_to_string()
g(c(mpg, hp))
#> [1] "mpg" "hp" 
g(mpg)
#> [1] "mpg"