spdl: A consistent C++ and R interface to spdlog
About
The RcppSpdlog repository (and CRAN package) provides access to the wonderful spdlog library along with the fmt library.
This permits use in C++ extensions for R by offering the spdlog (header-only) library
along with the (header-only) fmt library (by using
LinkingTo as described in Section
1.1.3 of WRE). More recently, RcppSpdlog was
extended so that it provides a set of key functions directly for use by
other R functions (as described in Section
5.4.3 of WRE).
However, now the use of, say, a debug logging message from C++ looks like
// in C++
spdlog::debug("Text with {} text {} which is {}", "auto", "expansion", 42);whereas in R, given the RcppSpdlog package and
namespace, it looks like this (if we use sprintf() to
assemble the message)
# in R
RcppSpdlog::log_debug(sprintf("Text with %s text %s which is %s", "auto", "expansion", 42L);and that irked us. Enter this package! By owning the
spld namespace (in R) and an easily overlayed namespace in
C++ of the same name we can do
// in C++
spdl::debug("Text with {} text {} which is {}", "auto", "expansion", 42);as well as (still using sprintf())
# in R
spdl::debug(sprintf("Text with %s text %s which is %s", "auto", "expansion", 42L));which is much better as it avoids context switching. Better still, with the internal formatter we can write the same format string as in C++ and not worry about format details:
# in R
spdl::debug("Text with {} text {} which is {}", "auto", "expansion", 42L);Details
We use a simple mechanism in which all R arguments are passed through
format() by default to render strings, and then pass a
single vector of strings argument through the restrictive C language
Foreign Function Interface to RcppSpdlog where
it can be passed to the C++ layer available there.
This also mean we use the fmt library in both languages
as the formatter. We prefer this is over other string-interpolating
libraries in R which are similar but subtly different. Should their use
be desired, they can of course be used: the default call to any of the
loggers is just a single-argument call with a text variable so users are
free to expand strings as they please. Anything starting from
paste and sprintf works.
Author
License
spdl is released under the GNU GPL, version 2 or later, just like R itself.