37 lines
1.1 KiB
Crystal
37 lines
1.1 KiB
Crystal
require "./lazy"
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require "./wrapper"
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module Spectator
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# Lazily stores a value of any type.
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# Combines `Lazy` and `Wrapper`.
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#
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# Contains no value until the first call to `#get` is made.
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# Any type can be stored in this wrapper.
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# However, the type must always be known when retrieving it via `#get`.
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# The type is inferred from the block, and all blocks must return the same type.
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# Because of this, it is recommended to only have `#get` called in one location.
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#
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# This type is expected to be used like so:
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# ```
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# @wrapper : LazyWrapper
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#
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# # ...
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#
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# def lazy_load
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# @wrapper.get { some_expensive_operation }
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# end
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# ```
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struct LazyWrapper
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@lazy = Lazy(Wrapper).new
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# Retrieves the value, if it was previously fetched.
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# On the first invocation of this method, it will yield.
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# The block should return the value to store.
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# Subsequent calls will return the same value and not yield.
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def get(& : -> T) : T forall T
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wrapper = @lazy.get { Wrapper.new(yield) }
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wrapper.get { yield }
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end
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end
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end
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