Lazy Finite or Infinite data in Widgets

Lazy_Finite_or_Infinite_data_in_Widgets.md

@@ -0,0 +1,60 @@
+# Lazy Finite or Infinite data in Widgets.
+
+## Summary
+
+A `DynamicData` Struc linked to a `DataLoader` than can fetch more data/trim its content based
+on received messages `FetchPrevious(how_many)`, `FetchNext(how_many)` / an update
+ call.
+
+Solves:
+  * Both Lazy Finite and Infinite `Scrollable`
+  * Both Lazy Finite and Infinite anything that uses a `Vec<Widgets>`
+  * Lower computation cost in both cases: Lazyness => smaller widget lists in
+  scope => fewer primitives calculated and simpler/quicker layout calculations.
+
+
+## Motivation
+
+Solves:
+  * Both Lazy Finite and Infinite `Scrollable`
+  * Both Lazy Finite and Infinite anything that uses a `Vec<Widgets>`
+  * Lower computation cost in both cases: Lazyness => smaller widget lists in
+  scope => fewer primitives calculated and simpler/quicker layout calculations.
+
+
+1. In Iced, large amounts of widget lists may cause performance issues due to the
+nature of update, draw, layout and view methods, even when many widgets are out
+of view, if states change.
+
+2. In Iced, I have not found Infinite list implementation where the
+very large/infinite list is only loaded partially when receiving requests.
+
+Seeing as 2. usually leads to 1. I propose a Struct that
+updates (grows, trims) an inner `data` field when requested. This `data` can
+subsequently be turned into Element(s) during the view() method call of the
+application.
+
+
+## Detailed Explanation
+
+
+A `DynamicData` Struc linked to a `DataLoader` than can fetch more data/trim its content based
+on received messages `FetchPrevious(how_many)`, `FetchNext(how_many)` / an update
+ call.
+
+
+Has a mutable buffer_size to let us choose how much to keep:
+* when at maximum capacity, `FetchPrevious(n)` pops `n` end values and inserts `n`
+new values at the start
+* when at maximum capacity, `FetchNext(n)` pops `n` start values and appends `n`
+new values at the end.
+
+Has an `OrderBy` trait that forces the Developper to define how to fetch more
+items (basically to now what **previous**, and **next** items are).
+
+
+The `DynamicData` struct exposes methods to change its capacity, its current
+position in the data, to ask the DataLoader to get more data in either direction.
+
+Since all these methods are public, the application can simply call them for any
+reason, for instance if it receives a button_pressed message.