R Under development (unstable) (2024-01-23 r85822 ucrt) -- "Unsuffered Consequences"
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> message("TESTING: Exception...")
TESTING: Exception...
> 
> library("R.oo")
Loading required package: R.methodsS3
R.methodsS3 v1.8.2 (2022-06-13 22:00:14 UTC) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.26.0 successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following object is masked from 'package:R.methodsS3':

    throw

The following objects are masked from 'package:methods':

    getClasses, getMethods

The following objects are masked from 'package:base':

    attach, detach, load, save

> oopts <- options(warn=1)
> 
> ######################################################################
> # 1. To catch a regular "error" exception thrown by e.g. stop().
> ######################################################################
> x <- NA
> y <- NA
> tryCatch({
+   x <- log(123)
+   y <- log("a")
+ }, error = function(ex) {
+   print(ex)
+ })
<simpleError in log("a"): non-numeric argument to mathematical function>
> print(x)
[1] 4.812184
> print(y)
[1] NA
> 
> 
> 
> ######################################################################
> # 2. Always run a "final" expression regardless or error or not.
> ######################################################################
> filename <- tempfile("R.methodsS3.example")
> con <- file(filename)
> tryCatch({
+   open(con, "r")
+ }, error = function(ex) {
+   cat("Could not open ", filename, " for reading.\n", sep="")
+ }, finally = {
+   close(con)
+   cat("The id of the connection is ",
+        ifelse(is.null(con), "NULL", con), ".\n", sep="")
+ })
Warning in open.connection(con, "r") :
  cannot open file 'D:\temp\RtmpO42xmH\R.methodsS3.example1e1782410643c': No such file or directory
Could not open D:\temp\RtmpO42xmH\R.methodsS3.example1e1782410643c for reading.
The id of the connection is 3.
> 
> 
> ######################################################################
> # 3. Creating your own Exception class
> ######################################################################
> setConstructorS3("NegativeLogValueException", function(
+   msg="Trying to calculate the logarithm of a negative value", value=NULL) {
+   extend(Exception(msg=msg), "NegativeLogValueException",
+     .value = value
+   )
+ })
> 
> setMethodS3("as.character", "NegativeLogValueException", function(this, ...) {
+   paste(as.character.Exception(this), ": ", getValue(this), sep="")
+ })
NULL
> 
> setMethodS3("getValue", "NegativeLogValueException", function(this, ...) {
+   this$.value
+ })
> 
> 
> mylog <- function(x, base=exp(1)) {
+   if (x < 0)
+     throw(NegativeLogValueException(value=x))
+   else
+     log(x, base=base)
+ }
> 
> 
> # Note that the order of the catch list is important:
> l <- NA
> x <- 123
> tryCatch({
+   l <- mylog(x)
+ }, NegativeLogValueException = function(ex) {
+   cat(as.character(ex), "\n")
+ }, "try-error" = function(ex) {
+   cat("try-error: Could not calculate the logarithm of ", x, ".\n", sep="")
+ }, error = function(ex) {
+   cat("error: Could not calculate the logarithm of ", x, ".\n", sep="")
+ })
> cat("The logarithm of ", x, " is ", l, ".\n\n", sep="")
The logarithm of 123 is 4.812184.

> 
> options(oopts)
> 
> message("TESTING: Exception...DONE")
TESTING: Exception...DONE
> 
> proc.time()
   user  system elapsed 
   0.28    0.07    0.34