knitr::opts_chunk$set( comment = "#>", tidy = FALSE, error = FALSE, fig.width = 8, fig.height = 8)
Debug R Packages
Specify debug messages as special string constants, and control debugging of
packages via environment variables. This package was largely influenced by
the debug
npm package.
Install the package from GitHub:
source("https://install-github.me/r-lib/debugme")
To use debugme
in your package, import it, and then add the following
.onLoad
function to your package:
.onLoad <- function(libname, pkgname) { debugme::debugme() }
You can now add debug messages via character literals. No function calls are necessary. For example:
"!DEBUG Start up phantomjs" private$start_phantomjs(phantom_debug_level) "!DEBUG Start up shiny" private$start_shiny(path) "!DEBUG create new phantomjs session" private$web <- session$new(port = private$phantom_port) "!DEBUG navigate to Shiny app" private$web$go(private$get_shiny_url())
The string literals are simply ignored when debugging is turned off. To
turn on debugging for a package, set the environment variable DEBUGME
to
the package name you want to debug. E.g. from a bash
shell:
export DEBUGME=mypackage
Or from within R:
Sys.setenv(DEBUGME = "mypackage")
Separate multiple package names with commas:
export DEBUGME=mypackage,otherpackage
The debug messages will be prefixed by the package names, and assuming your terminal supports color, will be colored differently for each package.
The debugme
debug strings may contain R code between backticks.
This code is evaluated at runtime, if debugging is turned on. A single
debug string may contain multiple backticked code chunks:
"!DEBUG x = `x`, y = `y`" if (x != y) { ...
I have always wanted a debugging tool that is very simple to use, can be controlled via environment variables, without changing anything it the packages themselves, * has zero impact on performance when debugging is off.
debugme
is such a tool.
Function calls are relatively cheap in R, but they still do have an impact.
If you never want to worry about the log messages making your code slower,
you will like debugme
. debugme
debug strings have practically no
performance penalty when debugging is off.
Here is a simple comparison between debugging with a function call, f1()
,
debugging with debug strings, f2()
and no debugging at all.
debug <- function(msg) { cat(msg, file = "/dev/null", "\n") } f1 <- function() { for (i in 1:100) { debug("foobar") Sys.sleep(.001) } }
f2 <- function() { for (i in 1:100) { "!DEBUG foobar" Sys.sleep(.001) } }
f3 <- function() { for (i in 1:100) { Sys.sleep(.001) } }
microbenchmark::microbenchmark(f1(), f2(), f3(), times = 10L)
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