Description:
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There appears to be a change in the behaviour of .= with typed properties, as compared to typeless properties.


The below script demonstrates a significant performance degradation with typed properties (in the ballpark of 2 orders of magnitude).

Test script:
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https://gist.github.com/dktapps/8a5d839f4c884f92d0b56f04c3b7d7d4

Expected result:
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The time per operation should only be slightly slower for typed properties than typeless properties (like it is for other things, like plain assignments).

Actual result:
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The time per operation is 2 orders of magnitude worse on the first loop than the second one.

On my machine, the script produces the following:
Typed property time: 8701.32 ns/op
Typeless property time: 211.446 ns/op