Computed Properties

v2 replaces most standalone computed properties with @expr: in RTML templates. For complex logic, use Go methods.

@expr: in Templates

Inline computed expressions that re-evaluate when their signal dependencies change:

<p>Doubled: @expr:Count.Get * 2</p>
<p>Positive: @expr:Count.Get > 0</p>
<p>Greeting: @expr:Name.Get + "!"</p>

Any Get() call inside @expr: creates a dependency. When the signal updates, only the affected expression re-renders.

Use then ... else for inline conditionals — reads naturally in templates:

<p>Status: @expr:Active.Get then "Online" else "Offline"</p>
<p>Tier: @expr:Count.Get > 10 then "high" else "low"</p>

Nested:

<p>Size: @expr:Count.Get > 100 then "XL" else Count.Get > 50 then "L" else "M"</p>

Legacy ? : syntax also works:

<p>Status: @expr:Active.Get ? "Online" : "Offline"</p>

Prefer then ... else for readability.

When @expr: isn’t enough, define a method on the struct:

type Stats struct {
    *core.HTMLComponent
    Scores *t.String
}

In RTML:

<p>Average: {Average}</p>

The {Method} syntax calls the method and injects the result.

Approach	Use for
`@expr:`	Simple arithmetic, comparisons, string concatenation
Go method + `{Method}`	Multi-step logic, loops, error handling
`state.Effect`	Side effects that react to signal changes

When you need to react to changes with side effects (logging, syncing, DOM manipulation), use state.Effect:

state.Effect(func() func() {
    val := count.Get()
    fmt.Println("count changed to", val)
    return nil
})

Effects re-run when any signal read inside them changes. Return a cleanup function if needed.