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Merge pull request #1538 from JL102/patch-1

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Fixed typos in CDE docs page, and added info on how config fragments in the chain can be overridden
This commit is contained in:
Jerry Zhao
2023-07-05 09:23:43 -07:00
committed by GitHub
parent e2f2951ff8 487009181e
commit 43789d77dd
1 changed files with 25 additions and 12 deletions
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37
docs/Advanced-Concepts/CDEs.rst
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@@ -21,24 +21,37 @@ Consider the following example using CDEs.
class WithX(b: Boolean) extends Config((site, here, up) => {
case SomeKeyX => b
}
})
class WithY(b: Boolean) extends Config((site, here, up) => {
case SomeKeyY => b
}
})
When forming a query based on a ``Parameters`` object, like ``p(SomeKeyX)``, the configuration system traverses the "chain" of config fragments until it finds a partial function which is defined at the key, and then returns that value.
.. code:: scala
val params = Config(new WithX(true) ++ new WithY(true)) // "chain" together config fragments
val params = new Config(new WithX(true) ++ new WithY(true)) // "chain" together config fragments
params(SomeKeyX) // evaluates to true
params(SomeKeyY) // evaluates to true
params(SomeKeyZ) // evaluates to false
In this example, the evaluation of ``params(SomeKeyX)`` will terminate in the partial function defined in ``WithX(true)``, while the evaluation of ``params(SomeKeyY)`` will terminate in the partial function defined in ``WithY(true)``. Note that when no partial functions match, the evaluation will return the default value for that parameter.
Config fragments take precedence from left to right, meaning that a fragment at the start of the chain can override the value of a fragment to the right. It helps to read the fragment chain from right to left.
.. code:: scala
case object SomeKeyX extends Field[Int](0)
class WithX(n: Int) extends Config((site, here, up) => {
case SomeKeyX => n
})
val params = new Config(new WithX(10) ++ new WithX(5))
println(params(SomeKeyX)) // evaluates to 10
The real power of CDEs arises from the ``(site, here, up)`` parameters to the partial functions, which provide useful "views" into the global parameterization that the partial functions may access to determine a parameterization.
.. note::
@@ -54,10 +67,10 @@ Site
class WithXEqualsYSite extends Config((site, here, up) => {
case SomeKeyX => site(SomeKeyY) // expands to site(SomeKeyY, site)
}
})
val params_1 = Config(new WithXEqualsYSite ++ new WithY(true))
val params_2 = Config(new WithY(true) ++ new WithXEqualsYSite)
val params_1 = new Config(new WithXEqualsYSite ++ new WithY(true))
val params_2 = new Config(new WithY(true) ++ new WithXEqualsYSite)
params_1(SomeKeyX) // evaluates to true
params_2(SomeKeyX) // evaluates to true
@@ -75,10 +88,10 @@ Here
class WithXEqualsYHere extends Config((site, here, up) => {
case SomeKeyY => false
case SomeKeyX => here(SomeKeyY, site)
}
})
val params_1 = Config(new WithXEqualsYHere ++ new WithY(true))
val params_2 = Config(new WithY(true) ++ new WithXEqualsYHere)
val params_1 = new Config(new WithXEqualsYHere ++ new WithY(true))
val params_2 = new Config(new WithY(true) ++ new WithXEqualsYHere)
params_1(SomeKeyX) // evaluates to false
params_2(SomeKeyX) // evaluates to false
@@ -95,10 +108,10 @@ Up
class WithXEqualsYUp extends Config((site, here, up) => {
case SomeKeyX => up(SomeKeyY, site)
}
})
val params_1 = Config(new WithXEqualsYUp ++ new WithY(true))
val params_2 = Config(new WithY(true) ++ new WithXEqualsYUp)
val params_1 = new Config(new WithXEqualsYUp ++ new WithY(true))
val params_2 = new Config(new WithY(true) ++ new WithXEqualsYUp)
params_1(SomeKeyX) // evaluates to true
params_2(SomeKeyX) // evaluates to false