为什么trace（...，edit = TRUE）在... = [.data.table [英] Why does trace(..., edit=TRUE) not work when ... = [.data.table

问题描述

要暂时编辑一个打包函数的主体 func ，我经常使用 trace（func，edit = TRUE）。因为某种原因，R不允许我在 func 是 [。data.table ：

To temporarily edit the body of a packaged function func, I frequently use trace(func, edit=TRUE). For some reason, though, R isn't letting me do this when func is [.data.table:

## Note: In this and the other cases below, once an editor pops up, I save and 
## and then exit without making any edits to the function. The commented-out
## message below each call to trace() is what is then printed to my R console.

trace("[.data.table", where=data.table, edit=TRUE)
# Error in .makeTracedFunction(def, tracer, exit, at, print, doEdit) : 
#   the editing in trace() can only change the body of the function, not 
#   the arguments or defaults

问题：可能是什么原因导致此错误？还有什么其他功能也触发呢？对于这样的函数，有没有一些替代的工作，将允许我编辑它们？

Questions: What might be causing this error? What other functions also trigger it? For such functions, is there some alternative work-around that will allow me to edit them?

FWIW，这似乎不是一些一般的问题， strong> data.table 的命名空间（参见下面的＃1 ）也不是子集方法的问题（参见例如＃2 ）。

FWIW, this doesn't seem to be some general issue with functions in data.table's namespace (see e.g. #1 below) nor is it an issue with subset methods in general (see e.g. #2 below).

## (#1)     
trace("within.data.table", where=data.table, edit=TRUE)
# Tracing function "within.data.table" as seen from package "data.table"
# [1] "within.data.table"

## (#2)
trace("[.Date", edit=TRUE)
# Tracing function "[.Date" in package "base"
# [1] "[.Date"

我正在运行 R-3.0.0 选项（editor =emacs），则会出现相同的错误，并且会出现同样的错误：c> and data.table_1.8.8 ，选项（编辑器=notepad）或使用R GUI的默认编辑器。

I am running R-3.0.0 and data.table_1.8.8 on a Windows XP machine, and get the same error whether I use set options(editor="emacs"), options(editor="notepad") or use the R GUI's default editor.

推荐答案

这显然是由于最近在<$ c $中的一个地方添加了大括号（即 {} c> data.table 的形式参数列表。

This is apparently being caused by the recent addition of curly braces (i.e. {}) at one place in data.table's formal argument list.

首先，MRE显示大括号真的导致 trace（...，edit = TRUE）到choke：

First, a MRE to show that braces really do cause trace(..., edit=TRUE) to choke:

## Without braces, no problem
func <- function(inColor=FALSE, col = if(inColor) "red" else "grey") { 
    plot(rnorm(99), col=col)}

trace(func, edit=TRUE)
# [1] "func"


## With braces, tracing fails
funcB <- function(inColor=FALSE, col = if(inColor) "red" else {"grey"}) { 
    plot(rnorm(99), col=col)}

trace(funcB, edit=TRUE)
# Error in .makeTracedFunction(def, tracer, exit, at, print, doEdit) : 
#   the editing in trace() can only change the body of the function, not 
#   the arguments or defaults

然后，对于记录，在版本1.8.6（对于其跟踪工作）和版本1.8.8（对于它不是）中：c $ c> [。data.table ]：

Then, for the record, here are the formals for [.data.table in versions 1.8.6 (for which tracing works) and version 1.8.8 (for which it doesn't):

## Version 1.8.6 -- Tracing worked
function (x, i, j, by, keyby, with=TRUE, nomatch=getOption("datatable.nomatch"), 
    mult="all", roll=FALSE, rolltolast=FALSE, 
    which=FALSE, .SDcols, verbose=getOption("datatable.verbose"), drop=NULL)


## Version 1.8.8 -- Tracing doesn't (See {} in the 'rollends' argument)
function (x, i, j, by, keyby, with=TRUE, nomatch=getOption("datatable.nomatch"), 
    mult = "all", roll = FALSE, 
    rollends = if (roll == "nearest") c(TRUE, 
        TRUE) else {
        if (roll >= 0) 
            c(FALSE, TRUE)
        else c(TRUE, FALSE)
    }, 
    which = FALSE, .SDcols, verbose = getOption("datatable.verbose"), 
    allow.cartesian = getOption("datatable.allow.cartesian"), 
    drop = NULL, rolltolast = FALSE) 

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