inject: Inject objects in an R expression

In hadley/rlang: Functions for Base Types and Core R and 'Tidyverse' Features

Inject objects in an R expression

Description

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).

Usage

inject(expr, env = caller_env())

Arguments

expr	An argument to evaluate. This argument is immediately evaluated in env (the current environment by default) with injected objects and expressions.
env	The environment in which to evaluate expr. Defaults to the current environment. For expert use only.

Examples

# inject() simply evaluates its argument with injection
# support. These expressions are equivalent:
2 * 3
inject(2 * 3)
inject(!!2 * !!3)

# 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)

# Injection with `!!!` splices lists of arguments in function
# calls:
args <- list(na.rm = TRUE, finite = 0.2)
inject(mean(1:10, !!!args))

hadley/rlang documentation built on Nov. 1, 2024, 4 p.m.