sym() creates a symbol from a string and
syms() creates a list of symbols from a
character vector.
enquo() and enquos()
delay the execution of one or several function arguments.
enquo() returns a single quoted expression, which is like
a blueprint for the delayed computation. enquos() returns
a list of such quoted expressions.
expr() quotes a new expression locally. It
is mostly useful to build new expressions around arguments
captured with enquo() or enquos():
expr(mean(!!enquo(arg), na.rm = TRUE)).
as_name() transforms a quoted variable name
into a string. Supplying something else than a quoted variable
name is an error.
That's unlike as_label() which also returns
a single string but supports any kind of R object as input,
including quoted function calls and vectors. Its purpose is to
summarise that object into a single label. That label is often
suitable as a default name.
If you don't know what a quoted expression contains (for instance
expressions captured with enquo() could be a variable
name, a call to a function, or an unquoted constant), then use
as_label(). If you know you have quoted a simple variable
name, or would like to enforce this, use as_name().
To learn more about tidy eval and how to use these tools, visit http://tidyeval.tidyverse.org and the Metaprogramming section of Advanced R.