vide/docs/tut/crash-course/8-implicit-effect.md

# Implicit Effects

Explicitly creating effects to update properties is tedious. You can
*implicitly* create an effect to update properties instead.

```lua
local create = vide.create
local source = vide.source

local function Counter()
    local count = source(0)

    return create "TextButton" {
        Activated = function()
            count(count() + 1)
        end,

        Text = function()
            return "count: " .. count()
        end
    }
end
```

This example is equivalent to the example seen on the previous page.

Instead of explicitly creating an effect, assigning a (non-event) property a
function will implicitly create an effect to update that property.

## Children

Children can also be set in a similar manner. A source passed as a child (passed
with a number key instead of string key) can return an instance or an array of
instances. An effect is automatically created to unparent removed instances and
parent new instances on source update.

```lua
local items = source {
    create "TextLabel" { Text = "A" }
}

local function List(props: { children: () -> { Instance } })
    return create "Frame" {
        create "UIListLayout" {},
        props.children
    }
end

local list = List { children = items } -- creates a list with a single text label "A"

items {
    create "TextLabel" { Text = "B" },
    create "TextLabel" { Text = "C" }
}

-- this will automatically unparent the text label "A", and parent the labels "B" and "C"
```