451cf3e2cd
The very first paragraph on "Package initialization" stated that "variables are initialized in declaration order, but after any variables they might depend on". This phrasing was easily misread as "declaration order is the first sorting criteria" and then contradicted what the subsequent paragraphs spelled out in precise detail. Instead, variable initialization proceeds by repeatedly determining a set of ready to initialize variables, and then selecting from that set the variable declared earliest. That is, declaration order is the second sorting criteria. Also, for the purpose of variable initialization, declarations introducing blank (_) variables are considered like any other variables (their initialization expressions may have side-effects and affect initialization order), even though blank identifiers are not "declared". This CL adds clarifying language regarding these two issues and the supporting example. Both gccgo and go/types implement this behavior. cmd/compile has a long-standing issue (#22326). The spec also did not state in which order multiple variables initialized by a single (multi-value) initialization expression are handled. This CL adds a clarifying paragraph: If any such variable is initialized, all that declaration's variables are initialized at the same time. This behavior matches user expectation: We are not expecting to observe partially initialized sets of variables in declarations such as "var a, b, c = f()". It also matches existing cmd/compile and go/types (but not gccgo) behavior. Finally, cmd/compile, gccgo, and go/types produce different initialization orders in (esoteric) cases where hidden (not detected with existing rules) dependencies exist. Added a sentence and example clarifying how much leeway compilers have in those situations. The goal is to preserve the ability to use static initialization while at the same time maintain the relative initialization order of variables with detected dependencies. Fixes #31292. Updates #22326. Change-Id: I0a369abff8cfce27afc975998db875f5c580caa2 Reviewed-on: https://go-review.googlesource.com/c/go/+/175980 Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com> |
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