Message-ID: <F0619D90-787A-435D-8192-726A64DF2003@me.com>
Date: 2014-07-21T15:20:42Z
From: Marc Schwartz
Subject: Question on Code snippet semantics
In-Reply-To: <53CD2CAD.6010503@oracle.com>
On Jul 21, 2014, at 10:07 AM, Mick Jordan <mick.jordan at oracle.com> wrote:
> I came across this code in library.R
>
> package <- as.character(substitute(package))
>
> where package is the first argument to the "library" function.
>
> I've been racking my brains to understand why this is not just an elaborate (and ineffcient) way to write:
>
> package <- "package"
>
> E.g.
>
> > package <- as.character(substitute(package))
> > package
> [1] "package"
> >
>
> Thanks
> Mick Jordan
Frequently used in a function body, where the function author wants the argument to be passed as an object name, rather than a character vector, or perhaps both, as is the case with library() and require().
For example:
test <- function(x) {as.character(substitute(x))}
# Quoted, passing "MyPackage" as a character vector
> test("MyPackage")
[1] "MyPackage"
# Not quoted, passing the object MyPackage
> test(MyPackage)
[1] "MyPackage"
In both cases, the argument passed as 'x' can then be used within the function as a character vector, rather than as the object itself.
Regards,
Marc Schwartz