bdd0e96d78
A block's value is now its last statement ONLY when that statement is a trailing expression with no `;`. A trailing `;` discards the value, leaving the block void. This makes value-vs-statement explicit and lets the compiler reject "this block was supposed to produce a value". Compiler: - Parser records `Block.produces_value` (last stmt is a no-`;` trailing expression) + `Block.discarded_semi` (the `;` that discarded a value), via `expectSemicolonAfter`. A trailing expression before `}` may now omit its `;` (previously a parse error). Match-arm and else-arm bodies are built value-producing regardless of the arm `;` (arms are exempt — the `;` is an arm terminator). - Lowering: `lowerBlockValue` / the block-expr path / `inferExprType` respect `produces_value`. A value-position block that discards its value is a hard error (`lowerValueBody` for function bodies; the value-context `.block` path for if/else branches, `catch` bodies, value bindings, match arms). Pure-failable `-> !` bodies (value rides the error channel) and a value-if whose branches are void are handled without false errors. - `defer`/`onfail` cleanup bodies lower as statements (void), so a trailing `;` there is fine. Migration (behavior-preserving — output unchanged): - stdlib + ~210 examples: dropped the trailing `;` on value-position last expressions. `format` now ends with an explicit `#insert "return result;"` (it relied on `#insert`-as-block-value, which `;` discards). - Two `main :: () -> s32` examples that relied on the old silent default-return got an explicit trailing `0`. - Rejection snapshots 0412 / 1013 regenerated (their quoted source lines lost a `;`); the diagnostics themselves are unchanged. Docs/tests: specs.md "Block values" section; examples 0040 (rules) + 0041 (rejection); 3 parser unit tests. Filed issue 0066 (pre-existing match-arm negated-literal phi-width quirk, surfaced not caused here). Gates: zig build, zig build test, run_examples.sh -> 343 passed, cross_compile.sh -> 7 passed (also refreshed its stale example names).
41 lines
1.1 KiB
Plaintext
41 lines
1.1 KiB
Plaintext
// `for` over a `List(T)` (a `{ items: [*]T, len, cap }` struct): value capture,
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// by-ref capture (mutates in place), iterating a `*List`, and a by-ref capture
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// used as a value-receiver method call (auto-deref).
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#import "modules/std.sx";
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Box :: struct {
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v: s64;
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boxed :: (self: Box) -> s64 { self.v } // value receiver
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}
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sum_ptr :: (xs: *List(s64)) -> s64 {
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total : s64 = 0;
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for xs: (n) { total = total + n; } // iterate through a *List
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total
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}
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main :: () -> s32 {
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xs := List(s64).{};
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xs.append(10);
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xs.append(20);
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xs.append(30);
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s : s64 = 0;
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for xs: (n) { s = s + n; } // value capture
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print("sum {}\n", s); // 60
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for xs: (*n) { n.* = n + 100; } // by-ref: writes back
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s = 0;
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for xs: (n) { s = s + n; }
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print("sum2 {}\n", s); // 360
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print("via ptr {}\n", sum_ptr(@xs)); // 360
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bs := List(Box).{};
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bs.append(.{ v = 7 });
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bt : s64 = 0;
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for bs: (*b) { bt = bt + b.boxed(); } // *Box receiver, value-self method
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print("boxes {}\n", bt); // 7
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0
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}
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