如何仅在满足条件时启动调试器 [英] How to start debugger only when condition is met

问题描述

假设我有一个函数，该函数使用整数 i 上的循环.现在出了点问题，我认为错误发生在 i = 5 时.现在，我可以逐步完成每一个步骤(到目前为止，我所做的事情).

Assume I have a function which uses a loop over integer i. Now something goes wrong and I assume the error happens when i=5. Now I can step through every single step (what I did up to now).

但是现在我了解了 browser 和 debug 的 condition 和 text 参数:

But now I read about the condition and text argument of browser and debug:

文本是可以在浏览器为已输入.
condition 条件，可以在浏览器中检索到输入.

text a text string that can be retrieved when the browser is entered.
condition a condition that can be retrieved when the browser is entered.

是否可以按照我想要的方式使用参数?

Is it possible to use the arguments in a way it works as I want?

这里是一个例子.调试器/浏览器应仅在达到 i = 5 后启动:

Here is an example. The debugger / browser should only start after i=5 is reached:

fun <- function(x, y, n) {
  result <- 0
  for (i in 1:n) {
    # browser(condition = (i == 5)) # does not work
    result <- result + i * ( x + y)
  }
  return(result)
}

x <- 2
y <- 3
n <- 10

# debug(fun, condition = (i == 5)) # does not work
debug(fun)
r <- fun(x, y, n)
print(r)

解决方案

if (i == 5) { # inside loop of fun()
  browser()
}

正在工作，但我想可能会有更好的选择(函数内没有多余的代码)

is working, but I thougt there might be something better (No extra code inside the function)

推荐答案

您可以在 browser()中使用参数 expr :

fun <- function(x, y, n) {
  result <- 0
  for (i in 1:n) {
    browser(expr = {i == 5})
    result <- result + i * ( x + y)
  }
  return(result)
}

如果表达式的计算结果为 TRUE ，则它将仅打开调用 browser()的环境.

It will then only open the environment where browser() was called from if the expression evaluates to TRUE.

如果要使用 debug():

debug(fun, condition = i == 5)

然后调用该函数:

fun <- function(x, y, n) {
  result <- 0
  for (i in 1:n) {
    result <- result + i * ( x + y)
  }
  return(result)
}

fun(x, y, n)

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