# \#interface

**URL:** https://racket.discourse.group/tag/interface/119.md

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## [Expressing contract conditions related to underlying data structures](https://racket.discourse.group/t/expressing-contract-conditions-related-to-underlying-data-structures/1707)

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**Author:** [@Balrrach](https://racket.discourse.group/u/Balrrach)\
**Replies:** 0\
**Last updated:** [February 12, 2023, 5:41pm UTC](https://racket.discourse.group/t/expressing-contract-conditions-related-to-underlying-data-structures/1707 "2023-02-12T17:41:55Z")

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Hello. I'm new to DbC and I'm trying to understand some of its fundamental concepts and how they could be applied to racket specifically. My questions is this: Suppose I want to define an interface. In order for the inte…

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## [Custom equality predicate - in struct/gen:equal+hash or extra function?](https://racket.discourse.group/t/custom-equality-predicate-in-struct-gen-equal-hash-or-extra-function/1086)

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**Author:** [@sschwarzer](https://racket.discourse.group/u/sschwarzer)\
**Replies:** 1\
**Last updated:** [June 19, 2022, 1:58am UTC](https://racket.discourse.group/t/custom-equality-predicate-in-struct-gen-equal-hash-or-extra-function/1086 "2022-06-19T01:58:12Z")

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Assuming you have a struct (struct foo (a b c) #:transparent) and you want a custom equality predicate. For example, two foo instances should be equal? if their corresponding a and b fields are equal?, regardless of …