[cel1ne]

I used extensions with multiple receivers for adding context inside data-structures.

Example: I have a layout-algorithm for a grid that takes sections:

    interface Section {
        val title: String
        fun something()
    }

Then I have the grid-algorithm. Inside I store expanded/collapsed state for each section. When I use a member-extension with both receivers I can write that pretty conveniently:

    class GridLayout(sections: List<Section>) {

        /* the state */
        val expandedSections = mutableSetOf<Section>()

        /* the extensions I need in this context */
        val Section.isExpanded get() = this@Section in expandedSections
  
        fun Section.expand() = expandedSections += this@Section

        
        fun compute() {
            ...
            if (!section1.isExpanded) {
                section2.expand()
            }
            ...
        }

    }

[fauigerzigerk]

This looks neither clear nor convenient to me.