rlang (version 0.1)

is_copyable: Is an object copyable?

Description

When an object is modified, R generally copies it (sometimes lazily) to enforce valuesemantics. However, some internal types are uncopyable. If you try to copy them, either with <- or by argument passing, you actually create references to the original object rather than actual copies. Modifying these references can thus have far reaching side effects.

Usage

is_copyable(x)

Arguments

x

An object to test.

Examples

# NOT RUN {
# Let's add attributes with structure() to uncopyable types. Since
# they are not copied, the attributes are changed in place:
env <- env()
structure(env, foo = "bar")
env

# These objects that can only be changed with side effect are not
# copyable:
is_copyable(env)

structure(base::list, foo = "bar")
str(base::list)

# In expressions, calls and pairlists are safely copyable. However,
# symbols are not:
structure(quote(foo), foo = "bar")
quote(foo)
# }