inject() evaluates an expression with injection
support. There are three main usages:
Splicing lists of arguments in a function call.
Inline objects or other expressions in an expression with !!
and !!!. For instance to create functions or formulas
programmatically.
Pass arguments to NSE functions that defuse their
arguments without injection support (see for instance
enquo0()). You can use {{ arg }} with functions documented
to support quosures. Otherwise, use !!enexpr(arg).
inject(expr, env = caller_env())An argument to evaluate. This argument is immediately
evaluated in env (the current environment by default) with
injected objects and expressions.
The environment in which to evaluate expr. Defaults to
the current environment. For expert use only.
# inject() simply evaluates its argument with injection
# support. These expressions are equivalent:
2 * 3
#> [1] 6
inject(2 * 3)
#> [1] 6
inject(!!2 * !!3)
#> [1] 6
# Injection with `!!` can be useful to insert objects or
# expressions within other expressions, like formulas:
lhs <- sym("foo")
rhs <- sym("bar")
inject(!!lhs ~ !!rhs + 10)
#> foo ~ bar + 10
#> <environment: 0x56240e4aa310>
# Injection with `!!!` splices lists of arguments in function
# calls:
args <- list(na.rm = TRUE, finite = 0.2)
inject(mean(1:10, !!!args))
#> [1] 5.5