I think the behavior is defined with the following statement in the spec: Primary expressions are the operands for unary and binary expressions.
x[0] is a primary expression, so it is the operand for the unary expression, thus the expression is avaluated as *(x[0]). On Thu, Jul 20, 2017 at 4:07 AM, Ian Lance Taylor <i...@golang.org> wrote: > On Wed, Jul 19, 2017 at 4:10 PM, <adrian.pr...@gmail.com> wrote: > > > > The EBNF specifies the syntax, not the behavior. EBNF does not indicate > the > > order of evaluation of source code, only the order of characters in the > > source code. > > Fair point. In this case it is also intended to indicate the > precedence. In fact, in every case I know of, it indicates the > precedence. > > Ian > > > On Wednesday, July 19, 2017 at 6:59:29 PM UTC-4, Ian Lance Taylor wrote: > >> > >> On Wed, Jul 19, 2017 at 3:28 PM, <adrian...@gmail.com> wrote: > >> > > >> > A question on Stack Overflow led me to carefully examine the spec and > I > >> > feel like there may be some detail that's missing - the behavior is > easy > >> > enough to work with, but it's effectively undefined according to the > >> > language spec. Specifically, with a variable x of type *[]string for > >> > example, *x[0] will not work because it is evaluated as *(x[0]), not > as > >> > (*x)[0]. This is unexpected based on the spec because the only > >> > specifications that could apply are the general order of evaluation, > which > >> > is left to right (not the case here), and operator precedence which > states > >> > that pointer dereference is a unary operator and unary operators have > >> > highest precedence (again clearly not what's happening). > >> > > >> > The closest it comes to explaining this behavior is in the section on > >> > address operators, which implies that the address operator & applies > to the > >> > entire slice expression next to it (or struct field selector, etc). > This > >> > leaves one to assume the same implication applies to the pointer > dereference > >> > operator as well. > >> > > >> > Is there something covering this that I glossed over reading the spec? > >> > If it's not just something I missed, is this worth clarifying in the > spec, > >> > without changing the behavior (purely a documentation change)? > >> > >> This is expressed in the EBNF grammar in the language spec. x[0] is a > >> PrimaryExpr. *x[0] is a unary_op applied to a PrimaryExpr. > >> > >> Ian > > > > -- > > You received this message because you are subscribed to the Google Groups > > "golang-nuts" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to golang-nuts+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
