18.6 Symbols

• A symbol represents the name of an object.
  • x
  • mtcars
  • mean.
• In base R, the terms symbol and name are used interchangeably (i.e. is.name() is identical to is.symbol()), but this book used symbol consistently because “name” has many other meanings.
• You can create a symbol in two ways:
  1. by capturing code that references an object with expr().
  2. turning a string into a symbol with rlang::sym():.

expr(x)
#> x

sym("x")
#> x

• A symbol can be turned back into a string with as.character() or rlang::as_string().
• as_string() has the advantage of clearly signalling that you’ll get a character vector of length 1.

as_string(expr(x))
#> [1] "x"

• We can recognise a symbol because it’s printed without quotes
• str() tells you that it’s a symbol, and is.symbol() is TRUE:

str(expr(x))
#>  symbol x

is.symbol(expr(x))
#> [1] TRUE

• The symbol type is not vectorised, i.e. a symbol is always length 1.
• If you want multiple symbols, you’ll need to put them in a list, using rlang::syms().