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Conditionals

Conditional Rendering

Views in Nago are plain Go values, so you build them with ordinary Go code. A few helpers make conditions and loops fit into a builder expression. Containers skip nil children, which is what If returns when the condition is false.

func orderView(order Order) core.View {
	return VStack(
		Text(order.Title).Font(HeadlineSmall),
		If(order.Shipped, Text("Shipped")),
		IfElse(order.Paid, Text("Paid"), Text("Payment pending")),
		IfFunc(order.HasInvoice, func() core.View {
			return invoiceView(order) // only built if HasInvoice is true
		}),
		VStack(
			ForEach(order.Items, func(item Item) core.View {
				return Text(item.Name)
			})...,
		).Alignment(Leading),
	).Alignment(Leading).Gap(L8)
}

Functions

FunctionDescription
If(b bool, t core.View) core.ViewReturns the view if b is true, otherwise nil.
IfElse(b bool, ifTrue, ifFalse core.View) core.ViewReturns one or the other view.
IfFunc(b bool, fn func() core.View) core.ViewLike If, but creates the view lazily, only if b is true.
ForEach[T, V any](seq []T, m func(T) V, more ...V) []VMaps each element of a slice to a view; more is appended at the end.
Each[T, V any](seq iter.Seq[T], m func(T) V, more ...V) []VLike ForEach, but for an iter.Seq.
Each2[K, V, X any](seq iter.Seq2[K, V], m func(K, V) X) []XMaps each key-value pair of an iter.Seq2.
With[T any](t T, with func(T) T) TPasses a value through a function, to intercept a builder chain without a local variable.

If, IfElse and IfFunc evaluate their arguments like any Go call: the views of If and IfElse are built even if they are not shown. Use IfFunc or Lazy when building a view is expensive or only valid under the condition.

Lazy views

Composable, also available as Lazy, is a func() core.View which implements core.View itself. It is evaluated only when it is rendered:

Lazy(func() core.View {
	return expensiveView()
})

Components with their own With method, like TStack.With, apply a function to themselves in the same way.

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