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Bug 22768 – lazy does not cache its results

Status: RESOLVED
Resolution: INVALID
Severity: enhancement
Priority: P1
Component: dmd
Product: D
Version: D2
Platform: All
OS: All
Creation time: 2022-02-13T12:30:27Z
Last change time: 2022-02-13T13:12:36Z
Assigned to: No Owner
Creator: Temtaime

Comments

Comment #0 by temtaime — 2022-02-13T12:30:27Z

import std; void foo(lazy string s) { s.writeln; s.writeln; } void main() { foo(() { 1.writeln; return `abc`; }()); } This simple program outputs: 1 abc 1 abc It should output instead: 1 abc abc

Comment #1 by stanislav.blinov — 2022-02-13T13:12:36Z

The spec does not mandate such behavior: https://dlang.org/spec/function.html#lazy-params The compiler *could* cache results if resulting delegate was strongly pure (https://dlang.org/spec/function.html#pure-functions #17), but even that is left up to the implementation, and `lazy` fails to infer attributes anyway.