54 lines
1.5 KiB
Crystal
54 lines
1.5 KiB
Crystal
module Spectator
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# Typeless wrapper for a value.
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# Stores any value or reference type.
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# However, the type must be known when retrieving the value.
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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 = Wrapper.new("wrapped")
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# value = wrapper.get(String)
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# ```
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struct Wrapper
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@pointer : Void*
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# Creates a wrapper for the specified value.
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def initialize(value)
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@pointer = Value.new(value).as(Void*)
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end
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# Retrieves the previously wrapped value.
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# The *type* of the wrapped value must match otherwise an error will be raised.
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def get(type : T.class) : T forall T
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@pointer.unsafe_as(Value(T)).get
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end
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# Retrieves the previously wrapped value.
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# Alternate form of `#get` that accepts a block.
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# The block must return the same type as the wrapped value, otherwise an error will be raised.
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# This method gets around the issue where the value might be a type (i.e. `Int32.class`).
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# The block will never be executed, it is only used for type information.
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#
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# ```
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# wrapper = Wrapper.new(Int32)
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# # type = wrapper.get(Int32.class) # Does not work!
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# type = wrapper.get { Int32 } # Returns Int32
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# ```
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def get(& : -> T) : T forall T
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@pointer.unsafe_as(Value(T)).get
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end
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# Wrapper for a value.
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# Similar to `Box`, but doesn't segfault on nil and unions.
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private class Value(T)
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# Creates the wrapper.
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def initialize(@value : T)
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end
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# Retrieves the value.
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def get : T
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@value
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end
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end
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end
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end
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