What is a Mixin?
A mixin is a reusable piece of functionality that you can “mix into” something else.
In Python, a class mixin adds behavior to a class:
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class LoggerMixin:
def log(self, msg):
print(msg)
class MyClass(LoggerMixin):
pass
Similarly, a colcon mixin adds a named group of arguments to a colcon command:
- Class mixin → adds behavior to code
- Colcon mixin → adds options to a command
Colcon Mixins allow you to apply a group of arguments under one name. For example:
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colcon build --mixin debug clang
This might expand to flags such as:
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--cmake-args -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
Note: Mixins are applied in the order listed. If two mixins set the same option, the later one overrides the earlier one.
Installation
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sudo apt install python3-colcon-mixin
How To Use Mixins
1. Define YAML Files
File structure:
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my_mixins/
├── index.yaml
├── debug.yaml
└── clang.yaml
index.yaml — maps mixin names to their files:
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build:
debug: debug.yaml
clang: clang.yaml
debug.yaml:
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arguments:
cmake-args:
- -DCMAKE_BUILD_TYPE=Debug
clang.yaml:
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arguments:
cmake-args:
- -DCMAKE_C_COMPILER=clang
- -DCMAKE_CXX_COMPILER=clang++
2. Register the Mixins
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colcon mixin add my_mixins /path/to/my_mixins/index.yaml
colcon mixin update
3. Verify
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colcon mixin show
4. Use
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colcon build --mixin debug clang
Useful Commands
Remove build artifacts for specific packages:
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# Remove a specific package
colcon clean packages -y --packages-select <package_name>
# Remove a package and all packages that depend on it
colcon clean packages -y --packages-up-to <package_name>
The --packages-up-to flag also works with mixins.
