Macros Overview

mevy provides three core macro families, each solving a different pain point in Bevy development. They’re designed to work together — use ui!{} to build UI bundles, code!{} for inline values, and entity!{} to spawn and manage entities.

Quick Reference

Macro	Purpose	Use when you need…
`code!{}`	Inline value construction	Hex colors, `Val`, `UiRect` without function calls
`ui!{}`	CSS-like UI bundles	Multiple UI components without boilerplate
`entity!{}`	Entity spawning & modification	Hierarchies, queries, and observers in one expression

When to Use Which

Just a color or value? → code!{}
A styled UI panel? → ui!{}
A complete entity with children? → entity!{}
All three together? → Use them together. entity!{} nests ui!{} naturally, and code!{} works inside both.

How They Work Together

entity!{
    <world>
    
    // ui!{} creates a bundle of UI components
    ui!((
        size: 100px 100px;
        background: #ff0000;
    ));
    
    // code!{} creates inline values
    BackgroundColor(code!{#00ff00});
    
    // Nested children with named entities
    [child][
        ui!(( size: 50px 50px; ));
        .observe(on_click);
    ]
}

Troubleshooting

“Missing bevy version” compile error

You need to specify the Bevy version feature in Cargo.toml:

mevy = { version = "0.3", features = ["0.18"] }

See Installation for the full list of supported versions.

Experimental features unexpectedly enabled

mevy_ecs has experimental as a default feature. To disable it:

mevy_ecs = { version = "0.2.4", default-features = false }

entity!{} — Entity spawning & modification
ui!{} — CSS-like UI notation
code!{} — Code replacement macro
Experimental Helpers — gere!, geco!, cen!, den!, wen!

Keyboard shortcuts

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