# Command/Observer which accepts a lambda
**URL:** https://discourse.itk.org/t/command-observer-which-accepts-a-lambda/2632
**Category:** Engineering
**Created:** [January 17, 2020, 7:28pm UTC](https://discourse.itk.org/t/command-observer-which-accepts-a-lambda/2632 "2020-01-17T19:28:21Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@blowekamp](https://discourse.itk.org/u/blowekamp)
#### Post date: [January 17, 2020, 7:28pm UTC](https://discourse.itk.org/t/command-observer-which-accepts-a-lambda/2632/1 "2020-01-17T19:28:21Z")
Hello,
I am wondering if anyone has already created a `itk::Command` class which accepts a C++ lambda function?
Otherwise, I am wondering if a new `itk::Object::AddObserver` method should be overloaded to accept `std::function ` so that a lambda can be directly added instead of constructing a command class.
What do you think?
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [January 17, 2020, 8:02pm UTC](https://discourse.itk.org/t/command-observer-which-accepts-a-lambda/2632/2 "2020-01-17T20:02:14Z")
Sounds like a great idea!
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### Author:  [@blowekamp](https://discourse.itk.org/u/blowekamp)
#### Post date: [March 30, 2020, 2:53pm UTC](https://discourse.itk.org/t/command-observer-which-accepts-a-lambda/2632/3 "2020-03-30T14:53:18Z")
I have implemented a similar thing in SimpleITK:
>
It is quite nice in C++, to easily be able to add a lambda function in nearly the same way as what has been done in Python.
I think we can add a similar feature to ITK in 5.2.
---
### Author:  [@blowekamp](https://discourse.itk.org/u/blowekamp)
#### Post date: [March 30, 2020, 10:03pm UTC](https://discourse.itk.org/t/command-observer-which-accepts-a-lambda/2632/4 "2020-03-30T22:03:26Z")
Here is an initial draft:
>
The original command callbacks had a signature of:
```auto
void f(const Object * caller, const EventObject & event)
```
With C++ lambdas, these are not really necessary, as those values can be specified in captures instead.
Here is the little test case of what’s implemented:
```auto
itk::Object::Pointer o = itk::Object::New();
int cnt = 0;
o->AddObserver(itk::AnyEvent(), [&cnt](const itk::EventObject &) { ++cnt; });
```
I think I am in favor of removing all the arguments for the std::function/lambda use cases. What do you think?