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By writing separate construction and assignment, plus the new feature of suppressing assignment to a member by writing `member = _ ;` (now allowed only in assignment operators). I do realize that's an "opt-out" which I normally prefer to avoid, but: - I considered and decided against (for now) the alternative of not having assignment be memberwise by default. I want to keep the (new to Cpp2) default of memberwise semantics for assignment as with construction. I think that's a useful feature, and normally if you do assign to a member it doesn't arise, and so I think it makes sense to explicitly call out when we're choosing not to do any assignment at all to a member before doing other assignment processing. We'll get experience with how it goes. - `_` is arguably natural here, since it's pronounced "don't care." There too, we'll see if that is natural generalized, or feels strained. For now it feels natural to me.
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| "8A27:1514" |
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@@ -4812,7 +4812,32 @@ class cppfront | |
| || found_default_init | ||
| ); | ||
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| // Emit the initializer if it it isn't '_' (don't care) and ... | ||
| if (initializer == "_") { | ||
| // I'll walk the walk: I've said publicly that _structured_ goto is perfectly | ||
| // kosher -- it's only _unstructured_ goto that's harmful (and Dijkstra knew it), | ||
| // which means: | ||
| // - jumping into a block or statement (I'm looking at you, Duff's Device) | ||
| // - jumping backwards (that's an unstructured loop == spaghetti control flow) | ||
| // - jumping across a variable declaration (C++ already bans this) | ||
| // | ||
| // But jumping forward-and-outward, skipping no declarations, is righteous. | ||
| // | ||
| // Here, using goto is the right tool for the job, and is better code because: | ||
| // - it avoids a gratuitous extra level of nesting inside an | ||
| // 'if (initializer != "_")' block of the next 100 lines (and please don't | ||
| // start the other diatribe about that the next 100 lines should be a | ||
| // separate named function - no it shouldn't) | ||
| // - which extra indent of identical code would make GitHub's diff for this | ||
| // commit super hard to read (diff does not deal well with blocks of code | ||
| // that simply change indentation level - in fact seeing that diff without | ||
| // the goto was the tipping point to just switch to goto here) | ||
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JohelEGP
Contributor
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| // ... but sadly I feel the need to defend it. | ||
| // | ||
| // As Scott would say (and has said), "so sue me" | ||
| // | ||
| goto skip_initializer; | ||
| } | ||
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| if (initializer.empty()) { | ||
| initializer = "{}"; | ||
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@@ -4909,6 +4934,8 @@ class cppfront | |
| separator = ", "; | ||
| } | ||
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| skip_initializer: ; | ||
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| // And on to the next data member... | ||
| ++object; | ||
| } | ||
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@@ -1190,22 +1190,30 @@ union: (inout t : meta::type_declaration) | |
| } | ||
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| // Add the destructor | ||
| t.add_member( " operator=: (move this) = { _destroy(); }" ); | ||
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| // Add default constructor | ||
| t.add_member( " operator=: (out this) = { }" ); | ||
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| // Add copy/move construction and assignment | ||
| (copy value_set: std::string = "") | ||
| { | ||
| for alternatives | ||
| do (a) { | ||
| value_set += " if that.is_(a.name)$() { set_(a.name)$( that.(a.name)$() ); }\n"; | ||
| } | ||
| value_set += " }\n"; | ||
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| t.add_member( std::string(" operator=: (out this, that) = {\n") | ||
| + " _storage = ();\n" | ||
| + " _discriminator = -1;\n" | ||
| + value_set | ||
| ); | ||
| t.add_member( std::string(" operator=: (inout this, that) = {\n") | ||
| + " _storage = _;\n" | ||
| + " _discriminator = _;\n" | ||
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gregmarr
Contributor
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| + value_set | ||
| ); | ||
| } | ||
| } | ||
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Oh, the "hide whitespace only changes" feature is only implemented in pull requests?