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https://github.com/ton-blockchain/ton
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With the introduction of nullable types, we want the compiler to be smart in cases like > if (x == null) return; > // x is int now or > if (x == null) x = 0; > // x is int now These are called smart casts: when the type of variable at particular usage might differ from its declaration. Implementing smart casts is very challenging. They are based on building control-flow graph and handling every AST vertex with care. Actually, I represent cfg not a as a "graph with edges". Instead, it's a "structured DFS" for the AST: 1) at every point of inferring, we have "current flow facts" 2) when we see an `if (...)`, we create two derived contexts 3) after `if`, finalize them at the end and unify 4) if we detect unreachable code, we mark that context In other words, we get the effect of a CFG but in a more direct approach. That's enough for AST-level data-flow. Smart casts work for local variables and tensor/tuple indices. Compilation errors have been reworked and now are more friendly. There are also compilation warnings for always true/false conditions inside if, assert, etc.
14 lines
311 B
Text
14 lines
311 B
Text
fun takeNullableTensor(mutate ij: (int, int)?) { }
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fun testSmartCastsDropAfterMutate() {
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var x: (int, int)? = (1, 2);
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return x.0; // ok
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takeNullableTensor(mutate x);
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return x.1; // error
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}
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/**
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@compilation_should_fail
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@stderr type `(int, int)?` is not indexable
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@stderr return x.1
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*/
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