[Proposal] Consider removing widget!() macro

[kivimango]

Context

Consider removing the widget!() macro in the next release.

Problem description & Solution

Pros:

• Improved build times
• Less bloated binary
• Simpler widget creation
• Generic widgets now could be created (ListView, TableView), see Generic widgets #322
• no inherited properties from the widget!() macro: widgets could be defined with components only that they use

Cons:

• More boilerplate code
• components registration in the build() method has to be done by programmatically
• creation of custom widgets may be more confusing to new developers -> need to be documented with examples

The structs would serve as a builder, just like now but without a macro call.
Probably the Template trait could be removed that too, but it would need to refactor the components/properties.

Examples and MockUps

For instance, the TextBlock could be defined and used as:

pub struct TextComponent {
    text: String
}

pub struct TextBlock {}
impl TextBlock {
     pub fn new(text: String) -> TextBlockBuilder {
        TextBlockBuilder::new(text)
    }
}

pub struct TextBlockBuilder {
    text: String
    
}
impl TextBlockBuilder {
    pub fn new(text: String) -> Self {
        self.text = text;
        self
    }
    
    pub fn build(bctx: &mut BuildContext) -> Entity {
        // create entity, then register its components with world
        let entity = bctx.create_entity();
        let text_component = TextComponent { text: self.text.clone() };
        bctx.register_component(entity, text_component);
        entity
    }
}

TextBlock::new("Sample text").build(bctx);

update: added cons

[trickypr]

Out of interest, would the usage of #[derive(...)] be a better fit than widget!()? At least from my rudimentary understanding of macros, it would function as a good alternative. It would probably solve the generic widgets problem and would be more familiar to most rust developers (I was very confused about the widgets macro when I first saw it). However, it would probably increase build times a bit and would have the same amount of bloat.

Mockup

#[derive(Debug, Clone, Default, AsAny)]
pub struct TextBlockState;

impl State for TextBlockState {
    // ...
}

#[derive(Widget)]
#[state(TextBlockState)] // My preferred solution for state, more complex to implement
struct TextBlock {
    // Another solution for state, although less clear to the reader
    #[state]
    state: TextBlockState,

    // Whatever else: ... 
}

impl Template for TextBlock {
    // ...
}

Docs

• Rust reference book