<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Mar 28, 2020, at 1:41 PM, David Blaikie <<a href="mailto:dblaikie@gmail.com" class="">dblaikie@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><blockquote class="gmail_quote" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;">><br class="">> But it doesn't - it means you write some generic code, test it with some cases & looks like it generalizes to other cases (you don't want to/can't test generic code with all possible generic arguments - that's why substitutability is important) then the code breaks when it hits a constant Value because it doesn't conform to the contract.<br class=""><br class="">It's not a break of the Liskov substitution principle, though.</blockquote><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><br class="">It does in the sense that all Values have a list of uses in the current API - yes, if you're proposing /changing the API/ so that Values don't have a use list API, that's one thing - but adding an assertion/runtime failure is not that. Having a runtime failure where by accessing the uses of /some/ Values is a contract violation/assertion failure/etc - that makes it not substitutable, you can't just treat all Values as equal & have to special case to avoid asking for the uses of some Values.<br class=""><br class="">Yes, if you move the use-list API down from Value, so Values don't have use lists, that's different/not what Chris is objecting to, I don't think - it was the " Making use-def chains work differently based on the dynamic type of a Value* is very problematic to me. " that was specifically the objection/liskov breaking issue.<br class=""> </div></div></blockquote></div><br class=""><div class="">Exactly, very well put David. I would be much less concerned if the use list apis were sunk out of Value, but I don’t see how that could be accomplished in a realistic way.</div><div class=""><br class=""></div><div class="">-Chris</div></body></html>