use generics to DRY up context code

pkg/gui/context/basic_view_model.go

@@ -0,0 +1,34 @@
+package context
+
+import "github.com/jesseduffield/lazygit/pkg/gui/context/traits"
+
+type BasicViewModel[T any] struct {
+	*traits.ListCursor
+	getModel func() []T
+}
+
+func NewBasicViewModel[T any](getModel func() []T) *BasicViewModel[T] {
+	self := &BasicViewModel[T]{
+		getModel: getModel,
+	}
+
+	self.ListCursor = traits.NewListCursor(self)
+
+	return self
+}
+
+func (self *BasicViewModel[T]) Len() int {
+	return len(self.getModel())
+}
+
+func (self *BasicViewModel[T]) GetSelected() T {
+	if self.Len() == 0 {
+		return Zero[T]()
+	}
+
+	return self.getModel()[self.GetSelectedLineIdx()]
+}
+
+func Zero[T any]() T {
+	return *new(T)
+}