Destructive Scopes

A scope can be marked as destructive using a :destructive tag after its declaration. Some examples:

• if:destructive()
• else:destructive
• else if:destructive
• match:destructive() { .. }
• case:destructive "condition" { .. }
• default:destructive { .. }

To understand destructive you first need to understand what a scope is in Evolve.

A destructive scope is effectively just a block of statements inside of render block.

We have 2 types of 'context' in Evolve: one that works exactly like C# and one that is a 'render' context that includes the additional evolve only things like state, enable slot etc. This Evolve context also lets you create UI elements like Something(attr:xyz, style = [@whatever], someParam = someExpression()) The other side of the coin is the C# context which is active inside a run block, or any delegate, or any method body, or any expression context.

Some scopes are implicitly destructive, such as those generated by a repeat. In the case of repeat, if the input size shrinks from one frame to another then the extra items that were inside the repeat last frame will be destroyed. If a repeat is disabled due to its parent scope being disabled, its child scopes will be disabled as normal and not be destroyed.

Destroying a View will destroy all of its descendent scopes and their associated elements.

template Example(required bool showGroup1) render {
    // because this scope is marked as destructive, if there is a frame in which
    // this branch is not entered, its descendents will all be destroyed instead of
    // being disabled as they normally would be. When the branch is later re-entered
    // the elements we be re-created again.
    if:destructive(showGroup1) {
        Text("Element 1");
        Text("Element 2");
    }
}