# Extending existing functionality

**URL:** <https://internals.rust-lang.org/t/extending-existing-functionality/1289>\
**Category:** ideas (deprecated)\
**Created:** [January 12, 2015, 6:18am UTC](https://internals.rust-lang.org/t/extending-existing-functionality/1289 "2015-01-12T06:18:47Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![jethrogb](https://avatars.discourse-cdn.com/v4/letter/j/43a26b/32.png) [@jethrogb](https://internals.rust-lang.org/u/jethrogb)\
**Post date:** [January 12, 2015, 8:55pm UTC](https://internals.rust-lang.org/t/extending-existing-functionality/1289/9 "2015-01-12T20:55:56Z")

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At compile time, you should be able to do this deterministically, yes?

Actually, I’m having trouble with this: the same issue that is preventing access in the example case above is preventing compile-time checks on the offset and size of such members.

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