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kotlinlang

1. I have `Set&lt;Project&gt;` where `Project`’s hash code is it’s ID (one of properties).
2. I wanted to updated `Project` stored in a `Set` with following code:
```
    override fun save(updatedProject: Project): Project {
        projects += updatedProject
        return updatedProject
    }
```
3. It turned out that I still have the old version of `Project` in a `Set` after this operation. But I want the new one to replace the old one.