我最初的猜測是,這是因爲方法分派圍巾警告
f = function(x) withCallingHandlers(x, warning=function(w) {
cat('muffled\n')
invokeRestart("muffleWarning")
})
然後
> withCallingHandlers(f(warning("f")), warning=function(w) message("caught"))
muffled
挖越深,實際的報警電話是在這個C堆棧跟蹤
#0 do_warning (call=0x3d4ad50, op=0x9c4bf0, args=0x45b9968, rho=0x45b9c40) at /home/mtmorgan/src/R-devel/src/main/errors.c:1140
#1 0x00000000004b4198 in bcEval (body=<optimized out>, rho=<optimized out>, useCache=<optimized out>) at /home/mtmorgan/src/R-devel/src/main/eval.c:4700
#2 0x00000000004bff40 in Rf_eval (e=0x3d45618, rho=0x45b9c40) at /home/mtmorgan/src/R-devel/src/main/eval.c:554
#3 0x00000000004c4e4d in Rf_applyClosure (call=0x45b8630, op=0x3d45730, arglist=<optimized out>, rho=0x9e7638, suppliedenv=0x9e7670) at /home/mtmorgan/src/R-devel/src/main/eval.c:1033
#4 0x00000000004c0005 in Rf_eval (e=0x45b8630, rho=0x9e7638) at /home/mtmorgan/src/R-devel/src/main/eval.c:670
#5 0x00000000004c0695 in forcePromise (e=0x45b9410) at /home/mtmorgan/src/R-devel/src/main/eval.c:458
#6 0x00000000004c0462 in Rf_eval (e=0xa1d338, rho=0x45b9368) at /home/mtmorgan/src/R-devel/src/main/eval.c:577
#7 0x000000000046fbfb in protectedEval (d=0x7fffffffc7f0) at /home/mtmorgan/src/R-devel/src/main/context.c:750
#8 0x0000000000470d48 in R_ToplevelExec (fun=0x46fbe0 <protectedEval>, data=0x7fffffffc7f0) at /home/mtmorgan/src/R-devel/src/main/context.c:705
#9 0x0000000000470de7 in R_tryEval (e=<optimized out>, env=<optimized out>, ErrorOccurred=0x7fffffffc89c) at /home/mtmorgan/src/R-devel/src/main/context.c:764
#10 0x0000000000470e26 in R_tryEvalSilent (e=<optimized out>, env=<optimized out>, ErrorOccurred=<optimized out>) at /home/mtmorgan/src/R-devel/src/main/context.c:787
#11 0x00007ffff49230b9 in R_dispatchGeneric (fname=0x44b37e8, ev=0x45b9368, fdef=0x45b92f8) at /home/mtmorgan/src/R-devel/src/library/methods/src/methods_list_dispatch.c:993
#12 0x00000000004f5337 in do_standardGeneric (call=<optimized out>, op=<optimized out>, args=<optimized out>, env=0x45b9368) at /home/mtmorgan/src/R-devel/src/main/objects.c:1167
....
其中在R_dispatchGeneric
方法調度的C代碼中是tryin摹通過評估找出類的參數,它
989 if(arg_sym == R_dots) {
990 thisClass = dots_class(ev, &check_err);
991 }
992 else {
993 PROTECT(arg = R_tryEvalSilent(arg_sym, ev, &check_err));
994 if(!check_err)
995 thisClass = R_data_class(arg, TRUE);
996 UNPROTECT(1); /* for arg */
997 }
這似乎是做來實現C級錯誤處理程序:
998 if(check_err)
999 error(_("error in evaluating the argument '%s' in selecting a method for function '%s': %s"),
1000 CHAR(PRINTNAME(arg_sym)),CHAR(asChar(fname)),
1001 R_curErrorBuf());
Rf_tryEvalSilent
評估在頂層,像在沒有建立調用處理程序的命令提示符;你可以在C代碼,其中處理器堆棧設置爲NULL
686 Rboolean R_ToplevelExec(void (*fun)(void *), void *data)
687 {
688 RCNTXT thiscontext;
689 RCNTXT * volatile saveToplevelContext;
690 volatile SEXP topExp, oldHStack;
691 Rboolean result;
692
693
694 PROTECT(topExp = R_CurrentExpr);
695 PROTECT(oldHStack = R_HandlerStack);
696 R_HandlerStack = R_NilValue;
697 saveToplevelContext = R_ToplevelContext;
看到這一點,因爲參數評測啓動,但不處理,一個變通辦法可能是
my_method(withCallingHandlers(warning('arrgh'), warning=function(w) ...))
但這可能是不實際的。
我有一個模糊的記憶,看到這個,或類似的東西,在R-dev郵件列表上討論過... – Spacedman