如何访问正在跟踪的函数的返回值 [英] How to access a return value of a function that is being traced
问题描述
我们有一个简单的功能
add10< - function(a){
a + 10
}
当调用add10退出时,我们想要调用一些函数。
trace.exit()< - function() {
...
}
跟踪设置如下。
trace(add10,exit = trace.exit)
我们打电话给add10
add10(5)
据了解,现在, trace.exit
将在 add10
完成执行后调用。有没有办法在 trace.exit
中访问 add10
的返回值?
我觉得应该有。但是,使用 sys.frames
并查看环境,我无法得到它。
这样做的原因是希望捕获对某些功能的所有调用,并返回给他们的值。
UPD 使用包装器或类似东西的解决方案是很好的,但是 trace
已经实现了一个装饰器模式,所以我的问题是关于从 trace
,而不是解决R中装饰器的问题。
不要使用一个显式地将返回值赋给一个局部变量的包装器:
add10< - function(a){
a + 10
}
wrap< - function(f){function(...){..ret < - f(...)}}
add10_wrap< - wrap(add10)
trace.exit< - function(){
cat(sprintf(返回值:%s\\\
,sys.frame(-1)$ .. ret))
}
trace(add10_wrap,exit = trace.exit)
add10_wrap(5)
一个缺点是包装器总是返回invisi结果 - 这就是为什么上面的例子只打印格式化的输出。
Is there any way of accessing return value of a function that is being traced by a function specified as exit param to trace? That sounds hard to understand, but I was not able to simplify the question without loosing the information. So here is a simple example.
We have a simple function
add10 <- function(a){
a + 10
}
And some function that we want to be called when call to add10 exits.
trace.exit() <- function(){
...
}
Tracing is set up the following way.
trace(add10, exit=trace.exit)
And we do a call to add10
add10(5)
As I understand of right now, trace.exit
will be called after add10
finished executing. Is there any way to access return value of add10
inside trace.exit
?
I feel that there should be. But playing with sys.frames
and looking through environments I was not able to get it.
The reason for doing so is a wish to capture all calls to some function and return values they give.
UPD Solution with wrapper or something similar is nice, but trace
already implements a decorator pattern, so my question is about accessing return value from trace
, not about solving the problem of decorators in R.
Why don't you use a wrapper that explicitly assigns the return value to a local variable:
add10 <- function(a){
a + 10
}
wrap <- function(f) { function(...) { ..ret <- f(...) } }
add10_wrap <- wrap(add10)
trace.exit <- function() {
cat(sprintf("Return value: %s\n", sys.frame(-1)$..ret))
}
trace(add10_wrap, exit=trace.exit)
add10_wrap(5)
One downside is that the wrapper will always return invisible results -- that's why the above example only prints the formatted output.
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