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33 lines
1.5 KiB
Markdown
33 lines
1.5 KiB
Markdown
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# Frequently asked questions
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## Why is it called salsa?
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I like salsa! Don't you?! Well, ok, there's a bit more to it. The
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underlying algorithm for figuring out which bits of code need to be
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re-executed after any given change is based on the algorithm used in
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rustc. Michael Woerister and I first described the rustc algorithm in
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terms of two colors, red and green, and hence we called it the
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"red-green algorithm". This made me think of the New Mexico State
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Question --- "Red or green?" --- which refers to salsa. Although this
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version no longer uses colors (we borrowed revision counters from
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Glimmer, instead), I still like the name.
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## What is the relationship between salsa and an Entity-Component System (ECS)?
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You may have noticed that Salsa "feels" a lot like an ECS in some
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ways. That's true -- Salsa's queries are a bit like *components* (and
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the keys to the queries are a bit like *entitites*). But there is one
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big difference: **ECS is -- at its heart -- a mutable system**. You
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can get or set a component of some entity whenever you like. In
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contrast, salsa's queries define **define "derived values" via pure
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computations**.
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Partly as a consequence, ECS doesn't handle incremental updates for
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you. When you update some component of some entity, you have to ensure
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that other entities' components are upated appropriately.
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Finally, ECS offers interesting metadata and "aspect-like" facilities,
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such as iterating over all entities that share certain components.
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Salsa has no analogue to that.
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