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40818cfe1c
Language clarification. The existing rules for selector expressions imply automatic dereferencing of pointers to struct fields. They also implied automatic dereferencing of selectors denoting methods. In almost all cases, such automatic dereferencing does indeed take place for methods but the reason is not the selector rules but the fact that method sets include both methods with T and *T receivers; so for a *T actual receiver, a method expecting a formal T receiver, also accepts a *T (and the invocation or method value expression is the reason for the auto-derefering). However, the rules as stated so far implied that even in case of a variable p of named pointer type P, a selector expression p.f would always be shorthand for (*p).f. This is true for field selectors f, but cannot be true for method selectors since a named pointer type always has an empty method set. Named pointer types may never appear as anonymous field types (and method receivers, for that matter), so this only applies to variables declared of a named pointer type. This is exceedingly rare and perhaps shouldn't be permitted in the first place (but we cannot change that). Amended the selector rules to make auto-deref of values of named pointer types an exception to the general rules and added corresponding examples with explanations. Both gc and gccgo have a bug where they do auto-deref pointers of named types in method selectors where they should not: See http://play.golang.org/p/c6VhjcIVdM , line 45. Fixes #5769. Fixes #8989. LGTM=r, rsc R=r, rsc, iant, ken CC=golang-codereviews https://golang.org/cl/168790043 |
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