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51 lines
1.1 KiB
Markdown
51 lines
1.1 KiB
Markdown
# Effects
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Effects are functions that are ran in response to source updates. They are
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called effects because they cause *side-effects* when reacting to source
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updates.
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Effects are created using `effect()`.
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```lua
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local source = vide.source
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local effect = vide.effect
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local count = source(0)
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effect(function()
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print("count: " .. count())
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end)
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-- "count: 0" printed
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count(1)
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-- "count: 1" printed
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```
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The callback given to `effect()` is ran immediately in a *reactive scope*. Any
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source read from inside a reactive scope will be tracked, so when any of those
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sources update, the effect will be reran too.
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Reactive scopes also track derived sources, it doesn't matter how deeply nested
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inside a function a source is.
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```lua
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local source = vide.source
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local effect = vide.effect
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local count = source(1)
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local doubled = function()
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return count() * 2
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end
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effect(function()
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print("doubled count: " .. doubled())
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end)
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-- "doubled count: 2" printed
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count(2)
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-- "doubled count: 4" printed
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```
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If a source is updated with the same value it already had, it will not rerun
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effects depending on it.
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