# Initialize empty list
**URL:** https://discourse.cmake.org/t/initialize-empty-list/2068
**Category:** Usage
**Created:** [October 25, 2020, 11:57am UTC](https://discourse.cmake.org/t/initialize-empty-list/2068 "2020-10-25T11:57:20Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@johan556](https://discourse.cmake.org/u/johan556)
#### Post date: [October 25, 2020, 11:57am UTC](https://discourse.cmake.org/t/initialize-empty-list/2068/1 "2020-10-25T11:57:20Z")
What is the most idiomatic way to initialize an empty list? I have earlier used
`set(mylist)`
This works, when I later starts to append items to the list. But I recently understood that this actually “unset” the variable. So I wonder if there is an idiomatically better way to initialize an empty list? Is setting it to an empty string better?
I have also noted in other circumstances that a list with just one element that is the empty string, somehow “collapses” into an empty list. If I for example:
- start with a list with three elements, the middle being an empty string ( “foo;;bar” )
- if I pop the last element, the length drops to 2
- if I now pop the first element, the length drops to 0 (not 1)
I guess having empty elements of a list is not common, so this is not a big “problem”. But it still feels irregular, and non-obvious.
Regards,
Johan Holmberg
---
### Author:  [@McMartin](https://discourse.cmake.org/u/McMartin)
#### Post date: [October 25, 2020, 3:17pm UTC](https://discourse.cmake.org/t/initialize-empty-list/2068/2 "2020-10-25T15:17:24Z")
Since a list is represented as a string, an empty list is an empty string:
```auto
set(mylist "")
```
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [October 25, 2020, 9:38pm UTC](https://discourse.cmake.org/t/initialize-empty-list/2068/3 "2020-10-25T21:38:14Z")
If you want to be absolutely sure that the variable will evaluate to an empty list (or empty string), use `set(mylist "")`. The reason is that unsetting a regular variable can unmask a cache variable of the same name. The following shows how this can happen:
```cmake
set(MyVar "Hi" CACHE STRING "" FORCE)
message("MyVar = ${MyVar}")
set(MyVar "Barry")
message("MyVar = ${MyVar}")
set(MyVar)
message("MyVar = ${MyVar}")
set(MyVar "")
message("MyVar = ${MyVar}")
```
When part of a project’s CMakeLists.txt file, the above would print the following:
```auto
MyVar = Hi
MyVar = Barry
MyVar = Hi
MyVar =
```
Note how using `set(MyVar)` unset the non-cache variable and re-exposed the cache variable of the same name again. Only after explicitly setting `MyVar` to an empty string did we manage to ensure `${MyVar}` evaluates to an empty value.